Method for printing three-dimensional items wtih semi-crystalline build materials

ABSTRACT

A method for printing a three-dimensional part with an additive manufacturing system includes providing a consumable feedstock material comprising a semi-crystalline polymer containing one or more secondary materials, wherein the consumable feedstock material has a process window in which crystalline kinetics are either accelerated or retarded. The consumable feedstock material is melted in the additive manufacturing system. At least a portion of the three-dimensional part from the melted consumable feedstock material in a build environment maintained within the process window.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims priority to and is a Continuation-in-Partof U.S. patent application Ser. No. 14/532,465 filed on Nov. 4, 2014which claims the benefit of U.S. Provisional Application No. 61/909,611,entitled “METHOD FOR PRINTING THREE-DIMENSIONAL PARTS WITHCRYSTALLIZATION KINETICS CONTROL”, and filed on Nov. 27, 2013, thecontents of both identified applications are incorporated herein intheir entireties.

BACKGROUND

The present disclosure relates to additive manufacturing techniques forprinting three-dimensional (3D) parts. In particular, the presentdisclosure relates to additive manufacturing methods for printing 3Dparts in a layer-by-layer manner from part materials having one or moresemi-crystalline polymeric materials. All references disclosed hereinare incorporated by reference.

Additive manufacturing systems are used to print or otherwise build 3Dparts from digital representations of the 3D parts (e.g., AMF and STLformat files) using one or more additive manufacturing techniques.Examples of commercially available additive manufacturing techniquesinclude extrusion-based techniques such as fused deposition modeling(FDM), electro-photography (EP), jetting, selective laser sintering(SLS), high speed sintering (HSS), powder/binder jetting, electron-beammelting, and stereolithographic processes. For each of these techniques,the digital representation of the 3D part is initially sliced intomultiple horizontal layers. For each sliced layer, a tool path is thengenerated, which provides instructions for the particular additivemanufacturing system to print the given layer.

For example, in an extrusion-based additive manufacturing system, a 3Dpart may be printed from a digital representation of the 3D part in alayer-by-layer manner by extruding a flowable part material. The partmaterial is extruded through an extrusion tip carried by a print head ofthe system, and is deposited as a sequence of roads on a substrate in anx-y plane. The extruded part material fuses to previously deposited partmaterial, and solidifies upon a drop in temperature. The position of theprint head relative to the substrate is then incremented along a z-axis(perpendicular to the x-y plane), and the process is then repeated toform a 3D part resembling the digital representation.

In fabricating 3D parts by depositing layers of a part material,supporting layers or structures are typically built underneathoverhanging portions or in cavities of 3D parts under construction,which are not supported by the part material itself. A support structuremay be built utilizing the same deposition techniques by which the partmaterial is deposited. The host computer generates additional geometryacting as a support structure for the overhanging or free-space segmentsof the 3D part being formed. Support material is then deposited from asecond nozzle pursuant to the generated geometry during the printingprocess. The support material adheres to the part material duringfabrication, and is removable from the completed 3D part when theprinting process is complete.

SUMMARY

An aspect of the present disclosure is directed to method for printing athree-dimensional part with an additive manufacturing system includesidentifying a semi-crystalline polymer to be used as a build materialfor an item to be printed. The crystalline kinetics of the buildmaterial are caused to be analyzed are obtained by heating the materialfrom a solid state to a melting point such that the build material ismelted and cooling the melted material until solidified. The methodincludes determining whether a secondary material is required to beadded to either retard or accelerate the crystalline kinetics of thebuild material. The crystallization kinetics of the build material withthe secondary material are obtained by heating the material from a solidstate to a melting point such that the build material is melted andcooling the melted material until solidified to identify a processingwindow for the additive manufacturing system. The method includesforming at least a portion of a layer of the three-dimensional part fromthe melted build material with the secondary material in a buildenvironment within the process window.

Another aspect of the present disclosure is directed to a method forprinting a three-dimensional item with an additive manufacturing system.The method includes identifying a semi-crystalline polymer to be used asa build material for an item to be printed that requires crystallinekinetics of the neat build material to be slowed. A sufficient amount ofthe secondary material is caused to be added to the build material toform a modified build material such that an enthalpy of the buildmaterial with the secondary material is between about 2 J/g heat offusion and about 80% of the heat of fusion of the build material that iscompositionally about 100 wt. % of the semi-crystalline build material,as measured by differential scanning calorimetry (DSC) when cooling fromthe melting temperature to the hot crystalline temperature at a rate of10° C./min. The crystalline kinetics of the build material with thesecondary material are obtained by heating the material from a solidstate to a melting point such that the build material is melted andcooling the melted material until solidified to identify a processingwindow for the additive manufacturing system. Process conditions areidentified within the process window such that the item can be printedwith a selected amount of crystallinity. At least a portion of a layerof the three-dimensional item is formed from the melted modified buildmaterial within the process window.

Another aspect of the present disclosure is directed to a method forprinting a three-dimensional item with an additive manufacturing system.The method includes identifying a semi-crystalline polymer to be used asa build material for an item to be printed that requires crystallinekinetics of the neat build material to be accelerated. A sufficientamount of the secondary material is caused to be added to the buildmaterial such that an enthalpy of the build material with the secondarymaterial is at least 5 J/g when cooled at 10° C./min cooling as measuredby differential scanning calorimetry (DSC) when cooling from the meltingtemperature to the hot crystalline temperature at a rate of 10° C./min.The crystalline kinetics of the build material with the secondarymaterial is analyzed by obtained by heating the material from a solidstate to a melting point such that the build material is melted andcooling the melted material until solidified to identify a processingwindow for the additive manufacturing system. Process conditions withinthe process window are identified such that the item can be printed witha selected amount of crystallinity. At least a portion of a layer of thethree-dimensional item formed from the melted modified build materialwithin the process window.

Another aspect of the present disclosure is directed to a method forprinting a three-dimensional item with a selective laser sinteringmanufacturing system. The method includes identifying a semi-crystallinepolymer to be used as a build material for an item to be printed thatrequires crystalline kinetics of the neat build material to be modified.A sufficient amount of the secondary material is caused to be added tothe build material to repress a hot recrystallization temperature by atleast about 3° C. which expands a temperature range between a melttemperature and the hot recrystallization temperature. Thecrystallization kinetics of the build material with the secondarymaterial is analyzed by obtained by heating the material from a solidstate to a melting point such that the build material is melted andcooling the melted material until solidified to identify a processingwindow between about the hot recrystallization temperature and about themelt temperature. At least a portion of a layer of the three-dimensionalitem formed from the melted modified build material within the processwindow.

Another aspect of the present disclosure is directed to a method forprinting a three-dimensional item with an out of oven additivemanufacturing system. The method includes identifying a semi-crystallinepolymer to be used as a build material for an item to be printed thatrequires crystalline kinetics of the neat build material to be slowed. Asufficient amount of the secondary material is caused to be added to thebuild material to form a modified build material such that an enthalpyof the build material with the secondary material is between about 2 J/gheat of fusion and about 80% of the heat of fusion of the build materialthat is compositionally about 100 wt. % of the semi-crystalline buildmaterial, as measured by differential scanning calorimetry (DSC) whencooling from the melting temperature to the hot crystalline temperatureat a rate of 10° C./min. A sufficient amount of plasticizer is added tothe suppress the glass transition temperature of the modified buildmaterial to ambient temperatures ranging between about 20° C. and about40° C. The crystalline kinetics of the modified build material areobtained by heating the material from a solid state to a melting pointsuch that the build material is melted and cooling the melted materialuntil solidified to identify a processing window for the additivemanufacturing system. Process conditions are identified within theprocess window such that the item can be printed with a selected amountof crystallinity. At least a portion of a layer of the three-dimensionalitem is formed from the melted modified build material within theprocess window.

Another aspect of the present disclosure includes a method for printinga three-dimensional part with an additive manufacturing system. Themethod includes providing a consumable feedstock material comprising asemi-crystalline polymer containing one or more secondary materials,wherein the consumable feedstock material has a process window in whichcrystalline kinetics are either accelerated or retarded. The consumablefeedstock material is melted in the additive manufacturing system. Atleast a portion of the three-dimensional part from the melted consumablefeedstock material in a build environment maintained within the processwindow.

Another of the present disclosure includes a method for printing athree-dimensional item with an additive manufacturing system. The methodincludes providing a consumable feedstock material comprising asemi-crystalline polymer containing one or more secondary materials thatare configured to retard crystallization of the one or moresemi-crystalline polymers, wherein the consumable feedstock material hasa process window in which crystalline kinetics are retarded and whereinthe consumable feed stock has an enthalpy of the consumable feedstock isbetween about 2 J/g heat of fusion and about 80% of the heat of fusionof the build material that is compositionally about 100% of thesemi-crystalline build material, as measured by differential scanningcalorimetry (DSC) when cooling from the melting temperature to the hotcrystalline temperature at a rate of 10° C./min. The consumablefeedstock is melted in the additive manufacturing system such that atleast a portion of the three-dimensional part is build from the meltedconsumable feedstock material in a build environment maintained withinthe process window.

Another aspect of the present disclosure includes method for printing athree-dimensional item with an additive manufacturing system. The methodincludes providing a consumable feedstock material comprising asemi-crystalline polymer containing one or more secondary materials thatare configured to retard crystallization of the one or moresemi-crystalline polymers, wherein the consumable feedstock material hasa process window in which crystalline kinetics are retarded and whereinthe consumable feed stock has an enthalpy of the consumable feedstock isat least 5 J/g when cooled at 10° C./min cooling as measured bydifferential scanning calorimetry (DSC) when cooling from the meltingtemperature to the hot crystalline temperature at a rate of 10° C./min.The consumable feedstock material is melted in the additivemanufacturing system that at least a portion of the three-dimensionalpart is build from the melted consumable feedstock material in a buildenvironment maintained within the process window.

An aspect of the present disclosure includes a method for printing athree-dimensional item with an additive manufacturing system. The methodincludes providing a consumable feedstock material comprising asemi-crystalline polymer containing one or more secondary materials thatare configured to retard crystallization of the one or moresemi-crystalline polymers, wherein the consumable feedstock material hasa process window in which crystalline kinetics in which a hotcrystallization temperature is suppressed at least 3° C. relative toneat semi-crystalline polymer. The consumable feedstock is melted in theadditive manufacturing system such that at least a portion of thethree-dimensional part is formed from the melted consumable feedstockmaterial in a build environment maintained within the process window.

DEFINITIONS

Unless otherwise specified, the following terms as used herein have themeanings provided below:

The term “polymer” refers to a polymeric material having one or moremonomer species, including homopolymers, copolymers, terpolymers, andthe like.

The term “semi-crystalline polymer” refers to a polymer capable ofexhibiting an average percent crystallinity in a solid state of at leastabout 10% by weight when allowed to crystallize to its fullest extent.The term “semi-crystalline polymer” includes polymeric materials capableof having crystallinities up to 100% (i.e., fully-crystalline polymericmaterials). The term “amorphous polymer” refers to a polymer that is nota semi-crystalline polymer.

Reference to “a” chemical compound refers one or more molecules of thechemical compound, rather than being limited to a single molecule of thechemical compound. Furthermore, the one or more molecules may or may notbe identical, so long as they fall under the category of the chemicalcompound. Thus, for example, “a” polyamide is interpreted to include oneor more polymer molecules of the polyamide, where the polymer moleculesmay or may not be identical (e.g., different molecular weights and/orisomers).

The terms “at least one” and “one or more of” an element are usedinterchangeably, and have the same meaning that includes a singleelement and a plurality of the elements, and may also be represented bythe suffix “(s)” at the end of the element. For example, “at least onepolyamide”, “one or more polyamides”, and “polyamide(s)” may be usedinterchangeably and have the same meaning.

Directional orientations such as “above”, “below”, “top”, “bottom”, andthe like are made with reference to a layer-printing direction of a 3Dpart. In the embodiments shown below, the layer-printing direction isthe upward direction along the vertical z-axis. In these embodiments,the terms “above”, “below”, “top”, “bottom”, and the like are based onthe vertical z-axis. However, in embodiments in which the layers of 3Dparts are printed along a different axis, such as along a horizontalx-axis or y-axis, the terms “above”, “below”, “top”, “bottom”, and thelike are relative to the given axis.

Unless otherwise specified, characteristics of a material or a 3D itemprinted from the material refer to the characteristics as measuredparallel to the orientation of the 3D item layers and perpendicular tothe layer-printing direction, and is referred to as an “xy-direction”.Correspondingly, the term “z-direction”, with reference tocharacteristics of a material or a 3D item printed from the materialrefer to the characteristics as measured perpendicular to theorientation of the 3D item layers and parallel to the layer-printingdirection. Unless the measurement direction is specified as “in thez-direction”, a measurement referred to herein is taken in thexy-direction. For example, a tensile strength of a 3D item of 10,000 psirefers to a tensile strength measured parallel to the layers of the 3Ditem. Alternatively, a tensile strength of a 3D item in the z-directionof 8,000 psi refers to a tensile strength measured perpendicular to thelayers of the 3D item.

Unless otherwise specified, temperatures referred to herein are based onatmospheric pressure (i.e. one atmosphere).

The term “additive manufacturing system” refers to a system that prints,builds, or otherwise produces 3D items and/or support structures atleast in part using an additive manufacturing technique. The additivemanufacturing system may be a stand-alone unit, a sub-unit of a largersystem or production line, and/or may include other non-additivemanufacturing features, such as subtractive-manufacturing features,pick-and-place features, two-dimensional printing features, and thelike.

The term “providing”, such as for “providing a consumable material”,when recited in the claims, is not intended to require any particulardelivery or receipt of the provided item. Rather, the term “providing”is merely used to recite items that will be referred to in subsequentelements of the claim(s), for purposes of clarity and ease ofreadability.

The terms “preferred” and “preferably” refer to embodiments of theinvention that may afford certain benefits, under certain circumstances.However, other embodiments may also be preferred, under the same orother circumstances. Furthermore, the recitation of one or morepreferred embodiments does not imply that other embodiments are notuseful, and is not intended to exclude other embodiments from the scopeof the present disclosure.

The terms “about” and “substantially” are used herein with respect tomeasurable values and ranges due to expected variations known to thoseskilled in the art (e.g., limitations and variabilities inmeasurements).

BRIEF DESCRIPTION OF THE DRAWINGS

Unless otherwise specified, the following terms as used herein have themeanings provided below:

The term “polymer” refers to a polymeric material having one or moremonomer species, including homopolymers, copolymers, terpolymers, andthe like.

The term “semi-crystalline polymer” refers to a polymer having anenthalpy of fusion of greater than 2 J/g, when measured from above themelting temperature to below the hot crystallization temperature. Theterm “amorphous polymer” refers to a polymer that is not asemi-crystalline polymer.

Reference to “a” chemical compound refers one or more molecules of thechemical compound, rather than being limited to a single molecule of thechemical compound. Furthermore, the one or more molecules may or may notbe identical, so long as they fall under the category of the chemicalcompound. Thus, for example, “a” polyamide is interpreted to include oneor more polymer molecules of the polyamide, where the polymer moleculesmay or may not be identical (e.g., different molecular weights and/orisomers).

The terms “at least one” and “one or more of” an element are usedinterchangeably, and have the same meaning that includes a singleelement and a plurality of the elements, and may also be represented bythe suffix “(s)” at the end of the element. For example, “at least onepolyamide”, “one or more polyamides”, and “polyamide(s)” may be usedinterchangeably and have the same meaning.

Directional orientations such as “above”, “below”, “top”, “bottom”, andthe like are made with reference to a layer-printing direction of a 3Dpart. In the embodiments shown below, the layer-printing direction isthe upward direction along the vertical z-axis. In these embodiments,the terms “above”, “below”, “top”, “bottom”, and the like are based onthe vertical z-axis. However, in embodiments in which the layers of 3Dparts are printed along a different axis, such as along a horizontalx-axis or y-axis, the terms “above”, “below”, “top”, “bottom”, and thelike are relative to the given axis.

Unless otherwise specified, characteristics of a material or a 3D itemprinted from the material refer to the characteristics as measuredparallel to the orientation of the 3D item layers and perpendicular tothe layer-printing direction, and is referred to as an “xy-direction”.Correspondingly, the term “z-direction”, with reference tocharacteristics of a material or a 3D item printed from the materialrefer to the characteristics as measured perpendicular to theorientation of the 3D item layers and parallel to the layer-printingdirection. Unless the measurement direction is specified as “in thez-direction”, a measurement referred to herein is taken in thexy-direction. For example, a tensile strength of a 3D item of 10,000 psirefers to a tensile strength measured parallel to the layers of the 3Ditem. Alternatively, a tensile strength of a 3D item in the z-directionof 8,000 psi refers to a tensile strength measured perpendicular to thelayers of the 3D item.

Unless otherwise specified, temperatures referred to herein are based onatmospheric pressure (i.e. one atmosphere).

The term “additive manufacturing system” refers to a system that prints,builds, or otherwise produces 3D items and/or support structures atleast in part using an additive manufacturing technique. The additivemanufacturing system may be a stand-alone unit, a sub-unit of a largersystem or production line, and/or may include other non-additivemanufacturing features, such as subtractive-manufacturing features,pick-and-place features, two-dimensional printing features, and thelike.

The term “providing”, such as for “providing a consumable material”,when recited in the claims, is not intended to require any particulardelivery or receipt of the provided item. Rather, the term “providing”is merely used to recite items that will be referred to in subsequentelements of the claim(s), for purposes of clarity and ease ofreadability.

The terms “preferred” and “preferably” refer to embodiments of theinvention that may afford certain benefits, under certain circumstances.However, other embodiments may also be preferred, under the same orother circumstances. Furthermore, the recitation of one or morepreferred embodiments does not imply that other embodiments are notuseful, and is not intended to exclude other embodiments from the scopeof the present disclosure.

The terms “about” and “substantially” are used herein with respect tomeasurable values and ranges due to expected variations known to thoseskilled in the art (e.g., limitations and variabilities inmeasurements).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of an additive manufacturing system configured toprint 3D items pursuant to the method of the present disclosure.

FIG. 2 is a front view of a print head of the additive manufacturingsystem.

FIG. 3 is an expanded sectional view of a drive mechanism, a liquefierassembly, and a nozzle of the print head.

FIG. 4 is an illustrative differential scanning calorimetry (DSC) plotof heat flow versus temperature for an exemplary build material.

FIG. 5 is an illustrative DSC plot of heat flow versus temperature foran exemplary build material of FIG. 4 modified with a secondarymaterial.

FIG. 6 is an illustrative DSC plot of heat flow versus temperature forPA6,6.

FIG. 7 is an illustrative DSC plot of heat flow versus temperature forPA6,6 base material of FIG. 6 modified with 25 wt. % PA 6-3T.

FIG. 8 is an illustrative DSC plot of heat flow versus temperature forthe PA6,6 base material of FIG. 6 modified with 50 wt. % PA 6-3T.

FIG. 9 is an illustrative DSC plot of heat flow versus temperature for abase co-polyester.

FIG. 10 is an illustrative DSC plot of heat flow versus temperature forthe base co-polyester of FIG. 9 modified with 10 wt. % PETG.

FIG. 11 is an illustrative DSC plot of heat flow versus temperature forthe base co-polyester of FIG. 9 modified with 20 wt. % PETG.

FIG. 12 is an illustrative DSC plot of heat flow versus temperature forthe base co-polyester of FIG. 9 modified with 30 wt. % PETG.

FIG. 13 is an illustrative DSC plot of heat flow versus temperature forthe base co-polyester of FIG. 9 modified with 15 wt. % PETG and 30 wt. %carbon fiber.

FIG. 14 is an illustrative DSC plot of heat flow versus temperature forthe base co-polyester of FIG. 9 modified with 10 wt. % PETG and 40 wt. %carbon fiber.

FIG. 15 is an illustrative DSC plot of heat flow versus temperature fora PEKK base material.

FIG. 16 is an illustrative DSC plot of heat flow versus temperature forthe PEKK base material of FIG. 15 modified with another PEKK material ata ratio of 2:1.

FIG. 17 is an illustrative DSC plot of heat flow versus temperature forthe PEKK base material of FIG. 15 modified with another PEKK material ata ratio of 3:2.

FIG. 18 is a flow chart of the disclosed method for control the kineticsof crystallization for semi-crystalline polymers.

FIG. 19 is a graphical representation of the half-crystalline timeversus temperature for several PEEK-PEI compositions.

FIG. 20 is a graphical illustration of storage modulus versustemperature for several PEKK based build materials.

FIG. 21 is a graphical illustration of modulus versus temperature forexemplary PET build materials, illustrating crystallization effects of apost-printing crystallization process.

FIG. 22 is a graphical illustration of high temperature profile of FIG.21 of modulus versus temperature for exemplary PET build materials,illustrating crystallization effects of a post-printing crystallizationprocess.

FIG. 23 is a graphical representation of modulus versus temperature forexemplary PET build materials, illustrating crystallization effects of apost-printing crystallization process

FIG. 24 is an illustrative DSC plot of heat flow versus temperature fora first polyester base material.

FIG. 25 is an illustrative DSC plot of heat flow versus temperature fora second polyester base material.

FIG. 26 is an illustrative DSC plot of heat flow versus temperature fora third polyester base material.

FIG. 27 is an electron-microscope photograph of an item printed withpolyamide under the trade designation PA 650 ng.

FIG. 28 is an electron-microscope photograph of an item printed withpolyethylene terephthalate (PET).

FIG. 29 is an electron-microscope photograph of an item printed with acopolymer of PA12 with TR90.

DETAILED DESCRIPTION

The present disclosure is directed to an additive manufacturing methodfor printing 3D items in a layer-by-layer manner from a build materialthat compositionally includes a blend of one or more semi-crystallinepolymers and one or more secondary materials. The combination of thesemi-crystalline polymer(s) and the secondary material(s) interact tocontrol the rate or kinetics at which crystallization occurs. Thecontrolled crystallization kinetics results in diminished forces andstresses relative to uncontrolled crystallization, such that layerscontaining semi-crystalline polymer(s) can be used to build an itemthrough additive manufacturing in a layer by layer manner thatpreviously could not be accomplished. Additionally, the controlled rateor kinetics at which crystallization occurs generates sufficient heat offusion or enthalpy to induce molecular reptation at the extrudate-iteminterface to bond the extruded layer to the item such that the layershave a sufficient bond to prevent de-lamination.

The disclosed method can be utilized to print an item with a number ofcommercially available semi-crystalline polymer(s) and/or co-polymer(s),including but not limited to, polyester(s), polyamide(s), such as, butnot limited to, nylon(s), polysulfone(s) and ketone(s), such as, but notlimited to, polyetheretherketone (PEEK), and polyetherketoneketone(PEKK) and combinations thereof. However, the disclosed method is notlimited to above the semi-crystalline polymer(s) and/or co-polymer(s),but rather the disclosed method can be utilized with anysemi-crystalline polymer(s) and/or co-polymer(s) having the capabilityof being utilized in an additive manufacturing device.

In some instances, depending upon the material desired to print theitem, the method involves controlling the crystallization kinetics ofthe semi-crystalline polymer(s) upon cooling from a melted state tominimize or otherwise reduce the percent crystallinity of the printeditem, while also generating sufficient crystallization-exothermic energyto induce molecular reptation at the extrudate-item interface. The rateof crystallinity can be reduced by providing a build material thatcompositionally includes one or more semi-crystalline polymers and oneor more secondary materials that are configured to retardcrystallization of the one or more semi-crystalline polymers, where theone or more secondary materials are substantially miscible with the oneor more semi-crystalline polymers. Additionally, direct polymerizationor selection of specially polymerized polymers, which are synthesizedwith disrupted structural regularity can be utilized that where themolecular structure limits and moderates their crystallization kineticsand mechanics.

In other instances, depending upon the material desired to print theitem, the method involves controlling the crystallization kinetics ofthe semi-crystalline polymer(s) to increase the kinetics or rate atwhich the crystals are formed upon cooling from a melted state, suchthat the item has a selected crystallinity while also generatingsufficient heat of fusion or enthropy to induce molecular reptation atthe extrudate-item interface. Typically, acceleration of thecrystallization kinetics is required when the semi-crystalline polymerin pure form exhibits less than 5 J/g enthalpy when cooled at 10° C./mincooling as measured by differential scanning calorimetry (DSC) whencooling from the melting temperature to the hot crystalline temperatureat a rate of 10° C./min. The acceleration of the crystallizationkinetics increases the enthalpy to at least 5 J/g when cooled at 10°C./min cooling as measured by differential scanning calorimetry (DSC)when cooling from the melting temperature to the hot crystallinetemperature at a rate of 10° C./min.

For instance, in FDM and EP additive manufacturing systems, accelerationof the crystallization kinetics allows the copolymer to be held within arange of the glass transition temperature and a cold crystallizationtemperature due to the development of small, but significant modulus andcrystallinity. Techniques for accelerating the kinetics of certainpolymers, such as certain polyketone and polyester copolymers includethe addition of micron-scale additives, such as synthetic fibers,minerals (natural or synthetic). The addition of one or more immisciblesecondary polymers, which are finely dispersed as a discrete phasethrough compounding techniques common in polymer processing can also beutilized to increase the crystallization kinetics.

In order to effectively induce molecular reptation at the extrudate-itemand sufficiently diminish the forces and stresses caused by volumetricshrinkage associated with typical crystallization of thesemi-crystalline polymer in a layer as it is cooled, a process window iscreated by slowing the crystallization kinetics such that where thepolymer(s) generate between about 2 J/g heat of fusion and about 80% ofthe heat of fusion of a build material that is compositionally about100% of the semi-crystalline build material, as measured by differentialscanning calorimetry (DSC) when cooling from the melting temperature tothe hot crystalline temperature at a rate of 10° C./min. Whenaccelerating the crystallization kinetics a minimum enthropy of about 5J/g is desired. The disclosed ranges represents a continuum of thepercentage of crystallinity in the build material where at the lower endof the range, the build material has properties more closely related tocrystalline materials and at the upper end of the range, the buildmaterial has properties more closely related to amorphous materials. Thedisclosed ranges also describe the range of useful entropy for unfilledmaterials at the low enthalpy and heavily filled materials, at the highenthalpy end of the range.

The manner in which the crystallization kinetics of the item materialare controlled can vary depending on the additive manufacturingtechnique used, such as an extrusion-based additive manufacturingtechnique including fused deposition modeling (FDM) and out of oven FDM(OOO), big area additive manufacturing (BAAM) andelectrophotography-based additive manufacturing technique (EP), which istypically between the glass transition temperature and a coldcrystallization temperature or a solidification temperature and the coldcrystallization temperature. A selective laser sintering technique (SLS)or a high speed sintering technique (HSS) use a different process windowin relative to extrusion-based additive manufacturing technique that istypically slightly above a hot crystallization temperature and slightlybelow a melt temperature. However, for HHS devices a process windowbetween the glass transition temperature and the cold crystallizationtemperature could be used for some materials. These distinctions areprimarily due to the different thermal states in which the printedlayers are typically held for the given additive manufacturingtechniques.

With respect to SLS and HSS additive manufacturing systems, thesecondary material or materials is utilized to retard or slow theavailability of the formation of crystallites. The retarding or slowingof the availability of the formation of crystallites can be caused byadding an amorphous polymer that is miscible with the semi-crystallinematerial and forms an amorphous alloy which lowers the hotcrystallization temperature. Alternatively, a monomer can be added asthe secondary material or materials to form a copolymer that breaks thelong range order of the polymer and hinders the availability of theformation of crystallites and therefore depresses the hotcrystallization temperature. The crystallites will maintain theirrespective energies required to break intermolecular bonds and hence themelting temperature of the alloy or copolymer will not changesignificantly.

However, the addition of the amorphous, miscible polymer or theirregular monomer with the semi-crystalline material will decrease thehot crystallization temperature and the rate at which the crystallitesform. While the amount of the secondary material will depend upon thepolymer class, the combination of the secondary material, whether anamorphous miscible polymer or an irregular monomer, will cause adepression in the hot crystallization temperature. However, thedepression or reduction of the hot cyrstallization temperature willallow the use of semi-crystalline materials in HSS and SLS additivemanufacturing devices that typically could not be utilized.

The secondary material represses the hot crystallization temperature atleast about 3° C. The secondary material represses the hotcrystallization temperature at least about 5° C. and more typically atleast about 10° C. The larger the repression of the hot crystallizationtemperature, the larger the processing window and the lower operatingtemperature can be, which can be advantageous especially when operatingan SLS or HSS device.

With respect to OOO devices, semi-crystalline materials similar to thatused in extrusion techniques are utilized. However a sufficient amountof plasticizer is added to reduce the glass transition temperature tobetween a range of 20° C. and about 45° C. such that the environment ofdoes not require heating. By reducing the glass transition temperature,lower residual stress are retained in the item manufactured by OOOdevices.

Fillers and reinforcing agents can be added to the polymer matrix toincrease the heat deflection temperature. For instance, after annealingthe item containing carbon fiber, significant increases in the heatdeflection temperature can be realized.

A non-limiting list of semi-crystalline polymers that can be utilizedincludes polycarpolactum PA6 and semicrystalline copolyester PET.However, other semi-crystalline polymers and secondary materials arealso contemplated.

By way of example, extrusion-based additive manufacturing systemstypically print or otherwise build 3D items from amorphous polymericmaterials, such as acrylonitrile-butadiene-styrene (ABS) resins andpolycarbonate resins. During a printing operation, the amorphouspolymeric material is melted and extruded as a series of roads, whichcool down to form layers of a 3D item. Due to the layer-by-layer natureof the printing, the cooling of each successive layer generates residualstresses in the 3D item, which are a function of the coefficient ofthermal expansion, percent shrinkage, and tensile modulus of thematerial. If not relieved, the residual stresses may physically distortthe 3D item, such as by causing the edges and corners of the 3D item tocurl up, referred to as “curl” or “curling”.

Amorphous polymeric materials have little or no ordered arrangements oftheir polymer chains in their solid states. As such, these materialsexhibit glass transition effects that can be controlled to partiallyrelieve residual stresses. For example, as disclosed in Batchelder, U.S.Pat. No. 5,866,058, an amorphous polymeric material may be depositedinto a heated chamber (or at least a locally-heat deposition region)maintained at a temperature that is between a solidification temperatureand a glass transition temperature of the material. This anneals thesuccessively-printed printed layers, allowing them to cool down andsolidify slowly, which can partially relieve the residual stresses.

Semi-crystalline polymeric materials, however, have different mechanicaland thermal characteristics from amorphous polymeric materials. Forexample, due to their achievable crystallinity, 3D items printed withsemi-crystalline polymeric materials may exhibit superior mechanicalproperties compared to 3D items printed with amorphous polymericmaterials. However, due to their higher levels of achievablecrystallinity, semi-crystalline polymeric materials can exhibitdiscontinuous changes in volume upon solidification. Therefore, layersof a semi-crystalline polymeric material may contract and shrink whendeposited, thereby accumulating inacceptable residual stresses.

In comparison to amorphous polymeric materials, which can haverelatively broad annealing windows, it has been conventionally difficultto maintain a temperature window that is suitable for annealingsemi-crystalline polymers, particularly with extrusion-based additivemanufacturing systems. For instance, curl will result if the polymer isheld at a temperature above or below the process window. Any variationsoutside of this small temperature window will result in solidificationwith discontinuous changes in volume, such as curl, if above or belowthe temperature window. The discontinuous changes in volume can beparticularly troublesome for extrusion-based additive manufacturingsystems where the printed 3D items or support structures are coupled tounderlying and non-shrinkable build sheets. Furthermore, sagging mayoccur if there is not enough crystallinity generated during the coolingprocess. Each of these conditions may result in distortions of theprinted 3D item. As such, it has been difficult to print dimensionallystable 3D items from semi-crystalline polymers using extrusion-basedadditive manufacturing systems, where the amount of crystallinity formedduring the cooling process is sufficient such that the 3D items do notsag, yet also do not induce curl forces that will curl the 3D item.

It is important that the crystallization kinetics are accurate andcorrect for the semi-crystalline material with the secondary material,otherwise a process window cannot be determined. In FDM manufacturingsystems, the whole item is built with partial crystallinity and thesupport materials are removed. After the support materials are removed,the item is annealed at a selected temperature for a selected amount oftime to congruently crystallize the part and prevent warping.

In SLS additive manufacturing, the item is built with build material inan amorphous state between hot crystallization temperature and below themelt temperature. The entire part is then cooled and crystallized in asingle step.

However, as discussed below, the crystallization kinetics of particularbuild materials can be controlled in an extrusion-based additivemanufacturing system to print 3D items having mechanical properties(e.g., strengths and ductilities) similar to those of semi-crystallinepolymeric materials, while also being annealable in a heated chamber ofan additive manufacturing system (or at least a locally-heateddeposition region) to partially relieve residual stresses.

FIGS. 1-3 illustrate system 10, which is an extrusion-based additivemanufacturing system for printing or otherwise building 3D items, fromthe build material blends discussed herein, in a manner that controlsthe crystallization kinetics, as discussed below. Suitableextrusion-based additive manufacturing systems for system 10 includefused deposition modeling systems developed by Stratasys, Inc., EdenPrairie, Minn. under the trademark “FDM”.

As shown in FIG. 1, system 10 may include chamber 12, platen 14, platengantry 16, print head 18, head gantry 20, and consumable assemblies 22and 24. Chamber 12 is an example enclosed build environment thatcontains platen 14 for printing 3D items and support structures, wherechamber 12 may be may be optionally omitted and/or replaced withdifferent types of build environments. For example, a 3D item andsupport structure may be built in a build environment that is open toambient conditions or may be enclosed with alternative structures (e.g.,flexible curtains).

In the shown example, the interior volume of chamber 12 may be heatedwith heater 12 h to reduce the rate at which the build and supportmaterials solidify after being extruded and deposited (e.g., to reducedistortions and curling). Heater 12 h may be any suitable device orassembly for heating the interior volume of chamber 12, such as byradiant heating and/or by circulating heated air or other gas (e.g.,inert gases). In alternative embodiments, heater 12 h may be replacedwith other conditioning devices, such as a cooling unit to generate andcirculate cooling air or other gas. The particular thermal conditionsfor the build environment may vary depending on the particularconsumable materials used.

In further embodiments, the heating may be localized rather than in anentire chamber 12. For example, the deposition region may be heated in alocalized manner. Example techniques for locally-heating a depositionregion include heating platen 14 and/or with directing heat air jetstowards platen 14 and/or the 3D items/support structures being printed).As discussed above, the heating in chamber 12 and/or the localizeddeposition region anneals the printed layers of the 3D items (andsupport structures) to partially relieve the residual stresses, therebyreducing curling of the 3D items.

Platen 14 is a platform on which 3D items and support structures areprinted in a layer-by-layer manner. In some embodiments, platen 14 mayalso include a flexible polymeric film or liner on which the 3D itemsand support structures are printed. In the shown example, print head 18is a dual-tip extrusion head configured to receive consumable filamentsfrom consumable assemblies 22 and 24 (e.g., via guide tubes 26 and 28)for printing 3D item 30 and support structure 32 on platen 14.Consumable assembly 22 may contain a supply of the build material forprinting 3D item 30 from the build material. Consumable assembly 24 maycontain a supply of a support material for printing support structure 32from the given support material.

Platen 14 is supported by platen gantry 16, which is a gantry assemblyconfigured to move platen 14 along (or substantially along) a verticalz-axis. Correspondingly, print head 18 is supported by head gantry 20,which is a gantry assembly configured to move print head 18 in (orsubstantially in) a horizontal x-y plane above chamber 12.

In an alternative embodiment, platen 14 may be configured to move in thehorizontal x-y plane within chamber 12, and print head 18 may beconfigured to move along the z-axis. Other similar arrangements may alsobe used such that one or both of platen 14 and print head 18 aremoveable relative to each other. Platen 14 and print head 18 may also beoriented along different axes. For example, platen 14 may be orientedvertically and print head 18 may print 3D item 30 and support structure32 along the x-axis or the y-axis.

System 10 also includes controller 34, which is one or more controlcircuits configured to monitor and operate the components of system 10.For example, one or more of the control functions performed bycontroller 34 can be implemented in hardware, software, firmware, andthe like, or a combination thereof. Controller 34 may communicate overcommunication line 36 with chamber 12 (e.g., with a heating unit forchamber 12), print head 18, and various sensors, calibration devices,display devices, and/or user input devices.

In some embodiments, controller 34 may also communicate with one or moreof platen 14, platen gantry 16, head gantry 20, and any other suitablecomponent of system 10. While illustrated as a single signal line,communication line 36 may include one or more electrical, optical,and/or wireless signal lines, allowing controller 34 to communicate withvarious components of system 10. Furthermore, while illustrated outsideof system 10, controller 34 and communication line 36 may be internalcomponents to system 10.

System 12 and/or controller 34 may also communicate with computer 38,which is one or more computer-based systems that communicates withsystem 12 and/or controller 34, and may be separate from system 12, oralternatively may be an internal component of system 12. Computer 38includes computer-based hardware, such as data storage devices,processors, memory modules and the like for generating and storing toolpath and related printing instructions. Computer 38 may transmit theseinstructions to system 10 (e.g., to controller 34) to perform printingoperations. Controller 34 and computer 38 may collectively be referredto as a controller assembly for system 10.

FIG. 2 illustrates a suitable device for print head 18, as described inLeavitt, U.S. Pat. No. 7,625,200. Additional examples of suitabledevices for print head 18, and the connections between print head 18 andhead gantry 20 include those disclosed in Crump et al., U.S. Pat. No.5,503,785; Swanson et al., U.S. Pat. No. 6,004,124; LaBossiere, et al.,U.S. Pat. Nos. 7,384,255 and 7,604,470; Batchelder et al., U.S. Pat. No.7,896,209; and Comb et al., U.S. Pat. No. 8,153,182. In additionalembodiments, in which print head 18 is an interchangeable, single-nozzleprint head, examples of suitable devices for each print head 18, and theconnections between print head 18 and head gantry 20 include thosedisclosed in Swanson et al., U.S. Patent Application Publication No.2012/0164256.

In the shown dual-tip embodiment, print head 18 includes two drivemechanism 40 and 42, two liquefier assemblies 44 and 46, and two nozzles48 and 50. In this embodiment the build material and the supportmaterial each preferably have a filament geometry for use with printhead 18. For example, as best shown in FIG. 3, the build material may beprovided as filament 52. In alternative embodiments, the build materialof the present disclosure may be provided in powder or pellet form foruse in an auger-pump print head, such as disclosed in Bosveld et al.,U.S. Publication No. 2013/0333798.

During operation, controller 34 may direct wheels 54 of drive mechanism40 to selectively draw successive segments filament 52 from consumableassembly 22 (via guide tube 26), and feed filament 52 to liquefierassembly 44. Liquefier assembly 44 may include liquefier tube 56,thermal block 58, heat shield 60, and tip shield 62, where liquefiertube 56 includes inlet end 64 for receiving the fed filament 52. Nozzle48 and tip shield 62 are accordingly secured to outlet end 66 ofliquefier tube 56, and liquefier tube 56 extends through thermal block58 and heat shield 60.

While liquefier assembly 44 is in its active state, thermal block 58heats liquefier tube 56 to define heating zone 68. The heating ofliquefier tube 56 at heating zone 68 melts the build material offilament 52 in liquefier tube 56 to form melt 70. The upper region ofliquefier tube 56 above heating zone 68, referred to as transition zone72, is not directly heated by thermal block 58. This generates a thermalgradient or profile along the longitudinal length of liquefier tube 56.

The molten portion of the build material (i.e., melt 70) forms meniscus74 around the unmelted portion of filament 52. During an extrusion ofmelt 70 through nozzle 48, the downward movement of filament 52functions as a viscosity pump to extrude the build material of melt 70out of nozzle 48 as extruded roads to print 3D item 30 in alayer-by-layer manner. While thermal block 58 heats liquefier tube 56 atheating zone 68, cooling air may also be blown through a manifold 76toward inlet end 64 of liquefier tube 56, as depicted by arrows 78. Heatshield 60 assists in directing the air flow toward inlet end 64. Thecooling air reduces the temperature of liquefier tube 56 at inlet end64, which prevents filament 52 from softening or melting at transitionzone 72.

In some embodiments, controller 34 may servo or swap liquefierassemblies 44 and 46 between opposing active and stand-by states. Forexample, while liquefier assembly 46 is servoed to its active state forextruding the support material to print a layer of support structure 32,liquefier assembly 44 is switched to a stand-by state to prevent thebuild material from being extruded while liquefier assembly 46 is beingused. After a given layer of the support material is completed,controller 34 then servoes liquefier assembly 46 to its stand-by state,and switches liquefier assembly 44 to its active state for extruding thebuild material to print a layer of 3D item 30. This servo process may berepeated for each printed layer until 3D item 30 and support structure32 are completed.

While liquefier assembly 46 is in its active state for printing supportstructure 32 from a support material filament, drive mechanism 42,liquefier assembly 46, and nozzle 50 (each shown in FIG. 2) may operatein the same manner as drive mechanism 40, liquefier assembly 44, andnozzle 48 for extruding the support material. In particular, drivemechanism 40 may draw successive segments of the support materialfilament from consumable assembly 24 (via guide tube 28), and feed thesupport material filament to liquefier assembly 46. Liquefier assembly46 thermally melts the successive segments of the received supportmaterial filament such that it becomes a molten support material. Themolten support material may then be extruded and deposited from nozzle50 as a series of roads onto platen 14 for printing support structure 32in a layer-by-layer manner in coordination with the printing of 3D item30.

As mentioned above, the build material compositionally includes a blendof one or more semi-crystalline polymers and one or more secondarymaterials that may either retard crystallization of the semi-crystallinepolymer(s) or accelerate the formation of crystals within the buildmaterial. When retarding crystallization, the secondary material(s)include one or more amorphous polymers that are at least partiallymiscible, and typically completely miscible, with the semi-crystallinepolymer(s). Also, the use of polymers with disrupted structuralregularity (or steric hindrance) that limits and moderates thecrystallization mechanics to retard crystallization. When acceleratingcrystallization, secondary materials are added that cause the formationof crystals including but not limited to, the addition of micro-scaleadditive such as synthetic fibers, natural or synthetic minerals, theaddition of immiscible secondary polymers that are dispersed as adiscrete phase through known compounding techniques. Again, whether thecrystallization kinetics are to be retarded or accelerated depends uponthe physical properties of the selected semi-crystalline buildmaterial(s).

FIG. 4 illustrates a DSC plot for an exemplary build material. The buildmaterial is nylon 12 under the trade designation Grivory® L16manufactured by EMS-Grivory business unit of EMS-Chemie AG, located atDomat/Ems, Switzerland. The DSC pot in FIG. 4 shows the various thermaltransitions that the next build material may exhibit. For example,during an initial heating phase, such as when the build material ismelted in liquefier assembly 44, the build material may produce aheating profile 80 with a glass transition temperature (T_(g)), a coldcrystallization temperature (T_(c,cold)), and a melting temperature(T_(m)). The glass transition temperature (T_(g)) refers to the pointalong curve 80 where the build material undergoes a second-ordertransition to achieve an increase in its heat capacity.

The cold crystallization temperature T_(c,cold) typically occurs due tothe increased mobility of the polymer molecules after exceeding theglass transition temperature T_(g), which allows a portion of thesemi-crystalline polymer(s) to form crystalline regions. Because thecrystallization is an exothermic process, it releases thermal energybased on a first-order transition, as illustrated by the inverted peakin heating profile 80.

The melting temperature T_(m) is the temperature at which the buildmaterial fully liquefies, also based on a first-order transition.Typically, the build material is quickly heated past its meltingtemperature T_(m) in liquefier assembly 44 for extrusion. As such,during this point in the process, the glass transition temperature T_(g)and the cold crystallization temperature T_(c,cold) are not overlyrelevant to the crystallization state of the extrudate, other than forpotential melt flow and temperature control aspects in liquefierassembly 44.

The DSC plot in FIG. 4 also includes a cooling profile 82, whichillustrates hot crystallization temperature T_(c,hot) and describes thecrystallization kinetics of the build material as it cools down from itsmelting temperature T_(m). For example, after being extruded from nozzle48, the extruded build material may deposit as roads onto thepreviously-formed layer of 3D item 30, and begin cooling down. In otherwords, the build material begins to follow cooling profile 82 at acooling rate that depends on the environment temperature that 3D item 30is printed in (e.g. in chamber 12), as well as the particularcomposition of the build material and the size of 3D item 30.

Preferably, the layers of 3D item 30 are printed in chamber 12 (or atleast in a locally-heated deposition region) that is maintained at atemperature between a solidification temperature and the coldcrystallization temperature T_(c,cold) of the build material. This cananneal the successively-printed printed layers, allowing them to cooldown and solidify slowly, which can partially relieve the residualstresses.

Referring to FIG. 5, the crystallization kinetics of the samesemi-crystalline material in FIG. 4, that includes a miscible amorphouspolymer which in this instance is Grilamid® TR 90 manufactured by EMS.TR 90 is a polyamide based on aliphatic and cycloaliphatic blocks andtherefore is amorphous and completely miscible in the base material.While the range 81 between glass transition temperature (T_(g)) and thecold crystallization temperature (T_(c,cold)), are slightly changed, thetemperature range 83 between the melting temperature T_(m) and the hotcrystallization temperature T_(c,hot) is increased, either by increasingthe melting temperature T_(m) or reducing the hot crystallizationtemperature T_(c,hot). The increase in the temperature range between themelting temperature T_(m) or reducing the hot crystallizationtemperature T_(c,hot) increases the operating window for additivemanufacturing techniques such as SLS and HSS.

Particularly beneficial results include the suppression or reduction ofthe hot crystallization temperature T_(c,hot), when using manufacturingtechniques such as SLS and HSS. The suppression or reduction of the hotcrystallization temperature T_(c,hot), allows the built item to beannealed at lower temperatures relative to those of semi-crystallinematerials that have not had the crystallization kinetics modified. Thesuppression of the hot crystallization temperature T_(c,hot), allows theannealing process to be performed at temperatures that are lower thanpreviously obtainable. As the removal of heat from the item being builtis a limiting factor in the size of the item being built through eitherthe SLS or HSS technique, the present disclosure provides the capabilityof increasing the size of the item being built with the SLS or HHStechnique, up to the doubling of the size of the item being builtrelative to currently used processes and materials.

When using extrusion-based additive techniques such as FDM, BAAM, andEP, chamber 12 or the locally-heated deposition region is maintained ata temperature between a solidification temperature and the glasstransition temperature T_(g) of the build material. These embodimentsare suitable for build materials having low levels of crystallineregions, where the crystalline regions are not capable of supporting theprinted layers at higher temperatures without slumping.

Alternatively, in other embodiments, chamber 12 or the locally-heateddeposition region is maintained at a temperature within an annealingwindow 84 having a lower limit at about the glass transition temperatureT_(g) of the build material and an upper limit that is less than thecold crystallization temperature T_(c,cold) of the build material. Inparticular, annealing window 84 preferably encompasses the plateauregion 86 of DSC heating curve 80, which is above the increased slopefor the glass transition temperature T_(g) and below the decreased slopefor the cold crystallization temperature T_(c,cold). These embodimentsare suitable for build materials having enough crystalline regions tosupport the printed layers without slumping, despite being held abovethe glass transition temperature T_(g) of the build material.

In further techniques, such as OOO, where low-temperature materials areused (e.g., those with glass transition temperatures near ambienttemperatures), chamber 12 may be omitted, and the build material may beprinted at room temperature (e.g., 25° C.). Regardless of the annealingtemperature, it has been found that the substantially-miscible blendsfor the build material modify the glass transition temperature T_(g) ofthe build material from that of the amorphous polymer(s), typicallyflowing the Flory-Fox Equation. The substantially-miscible blends mayalso decrease the hot crystallization temperature T_(c,hot) of the buildmaterial from that of the pure semi-crystalline polymer(s). Thisprovides a unique advantage in that the cumulative amount ofcrystallization for the build material upon cooling can be reduced,which accordingly allows the printed layers of the build material tohave low levels of crystallinity.

In particular, upon being extruded and deposited from nozzle 48, thebuild material preferably is quickly cooled down past its hotcrystallization temperature T_(c,hot) to its annealing temperature belowthe cold crystallization temperature T_(c,cold) of the build material(e.g., within annealing window 84). This effectively supercools thebuild material down below its cold crystallization temperatureT_(c,cold). It should also be noted that when sufficient amounts offiller such as, but not limited to glass and carbon fiber, items can beprinted in the cold crystallization temperature T_(c,cold) region,because the filler effectively retards the volumetric change duringcrystallization.

It has been found that the level of crystallinity can be controlledbased on the particular annealing temperature used. For instance, ifmore amorphous properties are desired, the annealing temperature may beset to be set within about 5° C. of the glass transition temperatureT_(g) of the build material. Alternatively, if more crystallineproperties are desired, the annealing temperature may be set to be setwithin 5° C. of the cold crystallization temperature T_(c,cold) of thebuild material. Furthermore, any intermediate amorphous-crystallinevariation may be achieved by maintaining the annealing temperature at aselected temperature within annealing window 84.

The incorporation of the amorphous polymer(s) also assists in physicallyimpeding the semi-crystalline polymer(s) from grouping together inordered arrangements to form crystalline regions. As such, as the buildmaterial quickly cools down from its melting temperature T_(m), theshort residence time in the region between its hot crystallizationtemperature T_(c,hot) and its cold crystallization temperatureT_(c,cold), combined with the crystallization impedance, preferablyminimizes or otherwise reduces the formation of crystalline regions inthe build material.

For instance, if a given pure semi-crystalline polymer (i.e., non-blend)is capable of crystallizing to its fullest extent in about 3 seconds inthe region between its hot crystallization temperature T_(c,hot) and itscold crystallization temperature T_(c,cold), and if it quickly coolsdown such that it resides in this region for about one second, it mayform about one-third of is achievable of crystalline regions. Incomparison, the crystallization impedance of the build material blendmay require more than a 10 to 20-fold increase in the time required tofully crystallize. As such, when the build material resides in thisregion between its hot crystallization temperature T_(c,hot) and itscold crystallization temperature T_(c,cold) for about one second, it mayonly form about 1-3% of its fully-achievable crystallinity, for example.In fact, it has been observed that the supercooled build materialexhibits a translucent, substantially non-opaque appearance. This is anindication that crystallinity has been significantly retarded sincecrystalline regions typically modify the indices of refraction of theextruded layers to render them opaque.

The minimized or reduced crystallization correspondingly reduces thediscontinuous changes in volume of the semi-crystalline polymer(s),thereby reducing the residual stresses on the printed layers.Furthermore, holding the printed layers at the annealing temperature(e.g., within annealing window 84) also anneals the successively-printedprinted layers, allowing them to cool down and solidify slowly, whichcan relieve the residual stresses typically associated with amorphousmaterials.

In other words, the build material is preferably supercooled quicklyfrom its extrusion temperatures down to an annealing temperature inannealing window 84, and then held within annealing window 84 for asuitable duration to relieve the residual stresses. After that, theprinted layers of the build material may be cooled down further (e.g.,below its glass transition temperature T_(g) and/or its solidificationtemperature).

Another interesting property of the build materials of the presentdisclosure is that, despite the minimized or reduced crystallinity, thecrystallization that does occur during the supercooling generates asufficient amount of heat to induce extra or increased molecularreptation at the extrudate-item interface. In other words, the heatproduced during the limited crystallization-exothermic reaction allowsthe polymer molecules at the extrudate-item interface to move and becomehighly entangled. It has been observed that, due to the heat of fusionof the extruded roads, the rate of temperature decay of the extrudedbuild material can change, and cool down at a slower rate. For example,in an interior raster pattern, this can result in an interfacialtemperature boost, causing better reptation in the X-Y build plane, aslong as the rastered roads contact each other before the extruded buildmaterial cools down to the annealing temperature in chamber 12. Thisaccordingly increases the strength of the printed 3D item 30 in both theintra-layer x-y directions, and also in the interlayer z-direction. As aresult, 3D item 30 may have mechanical properties (e.g., strengths andductilities) similar to those of semi-crystalline polymer(s). Also, ifthe material is maintained at a temperature above the glass transitiontemperature, the transition is not necessary to be overcome to impartmobility at the item-extrudate interface.

In extrusion based printing techniques other than OOO, and with HSS oncethe printing operation is completed, 3D item 30 may then be cooled downto room temperature and optionally undergo one or more post-printingprocesses. Alternatively, 3D item 30 may be reheated in a post-printingcrystallization step. In this step, 3D item 30 may be heated up to aboutits cold crystallization temperature T_(c,cold) for a sufficientduration to induce further crystallization of the semi-crystallinepolymer(s). Examples of suitable annealing durations in thepost-printing crystallization step range from about 30 minutes to 3hours, and may vary depending on the dimensions of each 3D item 30 andthe build material compositions. Correspondingly, examples of suitableannealing temperatures in the post-printing crystallization step rangefrom about the cold crystallization temperature T_(c,cold) of the buildmaterial to within about 10° C. above its cold crystallizationtemperature T_(c,cold), and more preferably to within about 5° C. aboveits cold crystallization temperature T_(c,cold).

The post-printing crystallization step can further increase themechanical, thermal, and chemical resistance properties of 3D item 30due to the increased formation of the crystalline regions. Additionally,this post-printing crystallization step is performed on 3D item 30 as awhole (i.e., congruent crystallization), rather than as the layers areindividually printed. As such, any potential shrinkage on 3D item 30from the formation of the crystalline regions occurs in a uniform mannersimilar to the effects in an injection molding process, rather than in alayer-by-layer manner that can otherwise result in curling effects.Another important feature with the post-printing crystallization step isthat 3D part 30 is preferably de-coupled from platen 14 (e.g., from abuild sheet of platen 14), allowing 3D part 30 to be furthercrystallized without being restricted by any non-shrinkable build sheetor rigid support material. However, a supporting sand or powder may beacceptable.

As mentioned above, a 3D part 30 having a translucent, substantiallynon-opaque appearance is an indication that crystallinity has beenretarded during the printing operation. Similarly, the transformationfrom the translucent, substantially non-opaque appearance to an opaqueappearance is an indication that the build material of 3D item 30 hasundergone significant crystallization in the post-printingcrystallization step. After the post-printing crystallization step iscompleted, the resulting 3D item 30 may then be cooled down to roomtemperature and optionally undergo one or more post-printing processes.

The post-printing crystallization step may be performed in chamber 12 ofsystem 10, or alternatively in a separate annealing oven. A separateannealing oven may be preferred in many situations, such as when supportstructure 32 needs to be removed prior to the post-printing annealingstep and/or when system 10 needs to be used for subsequent printingoperations. For example, a printing farm of multiple systems 10 mayoperate in coordination with one or more separate annealing ovens tomaximize the duty cycles of the systems 10.

The above-discussed control of the crystallization kinetics of the buildmaterial requires the build material to have a blend of one or moresemi-crystalline polymers and one or more secondary materials,preferably amorphous polymer(s), that retard crystallization of thesemi-crystalline polymer(s) and that are at least partially miscible (ormore preferably, substantially miscible) with the semi-crystallinepolymer(s).

Preferably the semi-crystalline polymer(s) and the secondary material(s)in the blend are separate compounds (e.g., separate polymers) that arehomogenously blended. However, in alternative (or additional)embodiments, build material may include one or more copolymers havingchain segments corresponding to the semi-crystalline polymer(s) and thesecondary material(s), where the chain segments of the secondarymaterial(s) retard the crystallization of the chain segments of thesemi-crystalline polymeric material(s).

Polyamides

The build material can include a polyamide build material thatcompositionally includes a polyamide blend of one or moresemi-crystalline polyamides, one or more amorphous polyamides, andoptionally, one or more additives dispersed in the polyamide blend. Thesemi-crystalline polyamide(s) may include polyamide homopolymers andcopolymers derived from monomers that include caprolactam, diamines incombination with monomers that include dicarboxylic acids, and mixturesthereof. The diamine monomers and the dicarboxylic acid monomers areeach preferably aliphatic monomers, and more preferably are each acyclicaliphatic monomers.

However, in other embodiments, the diamine monomers and/or thedicarboxylic acid monomers may include aromatic or cycloaliphatic groupswhile maintaining crystalline domains. Furthermore, in some embodiments,the semi-crystalline polyamide(s) may include cyclic groups in graftedpendant chains (e.g., maleated groups), as discussed below. Preferredpolyamide homopolymers and copolymers for the semi-crystallinepolyamide(s) may be represented by the following structural formulas:

where R₁, R₂, and R₃ may each be a hydrocarbon chain having 3-12 carbonatoms. The hydrocarbon chains for R₁, R₂, and R₃ may be branched (e.g.,having small alkyl groups, such as methyl groups) or unbranched, andwhich are preferably aliphatic, acyclic, saturated hydrocarbon chains.

As used herein, reference to a repeating unit identifier “n” in apolymer structural formula means that the bracketed formula repeats forn units, where n is a whole number that may vary depending on themolecular weight of the given polymer. Furthermore, the particularstructures of the bracketed formulas may be the same between therepeating units (i.e., a homopolymer) or may be vary between therepeating units (i.e., copolymer). For example, in the above-shownFormula 1, R₁ may be the same structure for each repeating unit toprovide a homopolymer, or maybe two or more different structures thatrepeat in an alternating copolymer manner, a random copolymer manner, ablock copolymer manner, a graft copolymer manner (as discussed below),or combinations thereof.

Preferred polyamides for the semi-crystalline polyamide(s) includenylon-type materials such as polycarpolactum (PA6),polyhexamethyleneaidpamide (PA6,6), polyhexamethylenenonamide (PA6,9),polyhexamethylenesebacamide (PA6,10), polyenantholactum (PA7),polyundecanolactum (PA11), polylaurolactam (PA12), and mixtures thereof.More preferably, the polyamides for the semi-crystalline polyamide(s)include PA6; PA6,6; and mixtures thereof. Examples of suitablesemi-crystalline polyamide(s) having aromatic groups includesemi-crystalline polyamides of aliphatic diamines and isophthalic acidand/or terephthalic acid (e.g., semi-crystalline polyphthalamides).

It has been discovered that the use of polyhexamethyleneaidpamide(PA6,6) provides a stronger and higher temperature semi-crystallinebuild material that both PA12 and PA 6, while costing significantly lessthan PA12. The PA6,6 can be blended with amorphous Nylon 6-3T to boostthe amorphous phase T_(g) and moderate or retard the rate ofcrystallization. Impact modifier, nucleating agents, stabilizers andfibrous fillers such as, but not limited to glass fibers or carbonfibers can be added to selectively improve the properties of the alloy.It should be noted that PA6,10 is a probable semi-crystalline buildmaterial for SLS applications, as PA6,10 has low moisture absorption anda lower operating window that can be achieved in current SLS units.

A DSC trace of PA6,6 is illustrated in FIG. 6. When 25 wt. % of PA 6-3Ris added to the PA6,6 a 15° C. decrease in the recrystallizationtemperature is realized as illustrated in FIG. 7. Referring to FIG. 8,the PA6-3T wt. % was increased to about 50 wt. % with about 50 wt. % ofthe PA6,6 which resulted a near elimination of the crystallinity of thealloy. FIGS. 6-8 illustrate that the manipulation of the secondarycompounds can effectively retard or control the rate of thecrystallization kinetics. Furthermore, in some embodiments, at least aportion of the semi-crystalline polyamide(s) are graft semi-crystallinepolyamide(s), each having a polyamide backbone and one or more impactmodifiers grafted to the backbone. The impact modifiers may includepolyolefin-chain monomers and/or elastomers having coupling groupsconfigured to graft the monomers to the polyamide backbone. Suitablecoupling groups for the impact modifiers include piperidine groups,acrylic/methacrylic acid groups, maleic anhydride groups, epoxy groups.

Preferred coupling groups include maleic anhydride groups and epoxygroups, such as those respectively represented by the followingstructural formulas:

where R₄ and R₅ may each be a hydrocarbon chain having 2-20 carbonatoms, and more preferably 2-10 carbon atoms; and where R₆ may be ahydrocarbon chain having 1-4 carbon atoms. The hydrocarbon chains of R₄,R₅, and R6 may each be branched or unbranched. For example, preferredimpact modifiers include maleated polyethylenes, maleatedpolypropylenes, and mixtures thereof. In embodiments in which the impactmodifier includes an elastomer, preferred impact modifiers includemaleated ethylene propylene diene monomers (EPDM).

Examples of suitable commercial impact modifiers include those availableunder the tradenames LOTADER from Arkema Inc., Philadelphia, Pa.; thoseunder the tradename ELVALOY PTW, FUSABOND N Series, and NUCREL from E.I. du Pont de Nemours and Company, Wilmington, Del.; and those under thetradename ROYALTURF from Chemtura Corporation, Philadelphia, Pa.Examples of preferred graft semi-crystalline polyamides include thosecommercially available under the tradename ULTRAMID from BASFCorporation, Florham Park, N.J.; and those under the tradename GRILAMIDfrom EMS-Chemie, Inc., Sumter, S.C. (business unit of EMS-Grivory).

The grafted impact modifiers may constitute from about 1% to about 20%by weight of the graft semi-crystalline polyamide(s). In someembodiments, the grafted impact modifiers constitute from about 5% toabout 15% by weight of the graft semi-crystalline polyamide(s). Inembodiments that incorporate the graft semi-crystalline polyamide(s),the graft semi-crystalline polyamide(s) may constitute from about 50% to100% by weight of the semi-crystalline polyamide(s) in the buildmaterial, more preferably from about 80% to 100% by weight, and evenmore preferably from about 95% to 100% by weight. In some preferredembodiments, the semi-crystalline polyamide(s) of the PA materialconsist essentially of the graft semi-crystalline polyamide(s).

The semi-crystalline polyamide(s) preferably have a molecular weightrange that renders them suitable for extrusion from print head 18, whichmay be characterized by their melt flow indices. Preferred melt flowindices for the semi-crystalline polyamide(s) range from about 1 gram/10minutes to about 40 grams/10 minutes, more preferably from about 3grams/10 minutes to about 20 grams/10 minutes, and even more preferablyfrom about 5 grams/10 minutes to about 10 grams/10 minutes where themelt flow index, as used herein, is measured pursuant to ASTM D1238-10with a 2.16 kilogram weight at a temperature of 260° C.

The PA material also compositionally includes one or more amorphouspolyamides that are preferably miscible with the semi-crystallinepolyamide(s). The amorphous polyamide(s) may include polyamidehomopolymers and copolymers derived from monomers that include diaminesin combination with monomers that include dicarboxylic acids, which arepreferably cycloaliphatic and/or aromatic monomers. However, in otherembodiments, the diamine monomers and/or the dicarboxylic acid monomersmay include aliphatic groups (e.g., acyclic aliphatic groups) whilemaintaining amorphous properties.

Preferred polyamide homopolymers and copolymers for the amorphouspolyamide(s) may be represented by the following structural formulas:

where R₇ and R₁₀ may each be a hydrocarbon chain having 3-12 carbonatoms. The hydrocarbon chains for R₇ and R₁₀ may be branched (e.g.,having small alkyl groups, such as methyl groups) or unbranched, andwhich are preferably aliphatic, acyclic, saturated hydrocarbon chains.In comparison, R₈, R₉, R₁₁, and R₁₂ may each be a hydrocarbon chainhaving 5-20 carbon atoms, which may be branched (e.g., having alkylgroups, such as methyl groups) or unbranched, and each of which includesone or more aromatic groups (e.g., benzene groups), one or morecycloaliphatic groups (e.g., cyclohexane groups), or combinationsthereof.

Preferred polyamides for the amorphous polyamide(s) include nylon-typematerials such as polyamides of hexamethylenediamine, isophthalic acid,terephthalic acid, and adipic acid (PA6i/6T); polyamides of PA12;3,3-dimethyl-4,4-diaminodicyclohexylmethane, and isophthalic acid(PA12/MACMI); polyamides of PA12;3,3-dimethyl-4,4-diaminodicyclohexylmethane, and terephthalic acid(PA12/MACMT); (PA12/MACMI/MACMT); PA6i; PA12/MACM36; PANDT/INDT;polyamides of trimethylhexamethylenediamine and terephthalic acid(PA6/3T); polyamides of cycloaliphaticdiamine and dodecanedioic acid;amorphous polyamides of aliphatic diamines and isophthalic acid and/orterephthalic acid (e.g., amorphous polyphthalamides); and mixturesthereof. More preferably, the polyamides for the amorphous polyamide(s)include PA6/3T, polyamides of cycloaliphaticdiamine and dodecanedioicacid, and mixtures thereof.

It is contemplated that 2,4,4 trimethyl diacid can be polymerized withPA6,10 to product a polymer that would have a high melting portion and ahindered recrystallization rate and temperature. The irregularity of the2,4,4 methyl groups hinders the ability of the PA6,10 to formcrystallites because the 2,4,4 trimethyl diacid displaces the abilityfor intermolecular and intramolecular bonding to occur. Adding 2,4,4trimethyl diacid monomer to the PA6,10 will hinder the ability of thepolymer to form crystallites. However, the crystallites that do formwill have the same level of energy needed to debind or break theintermolecular and intramoleular boding and obtain flow.

In some embodiments, at least a portion of the amorphous polyamide(s)may be graft amorphous polyamide(s), each having a polyamide backboneand one or more impact modifiers grafted to the backbone. Preferredimpact modifiers for grafting to the amorphous polyamide(s) includethose discussed above for the graft semi-crystalline polyamide(s), suchas polyolefin-chain monomers and/or elastomers having coupling groupsconfigured to graft the monomers to the polyamide backbone (e.g.,piperidine groups, acrylic/methacrylic acid groups, maleic anhydridegroups, and epoxy groups). Suitable concentrations of the grafted impactmodifiers in the graft amorphous polyamide(s), and suitableconcentrations of the graft amorphous polyamides relative to theentirety of amorphous polyamide(s) in the build material include thosediscussed above for the graft semi-crystalline polyamide(s).

Preferred concentrations of the amorphous polyamide(s) in the polyamideblend range from about 30% to about 70% by weight, more preferably fromabout 40% to about 60% by weight, and even more preferably from about45% to about 55% by weight, where the semi-crystalline polyamide(s)constitute the remainder of the polyamide blend for use in extrusionbased devices, EP and cooled SLS. Accordingly, preferred ratios of theamorphous polyamide(s) to the semi-crystalline polyamide(s) range fromabout 3:7 to about 7:3, more preferably from about 4:6 to about 6:4, andeven more preferably from about 4.5:5.5: to about 5.5:4.5. Preferredconcentrations of the amorphous polyamide(s) in the polyamide blendrange from about 5% to about 20% by weight and about 80% to about 95% byweight of the semi-crystalline polyamide when used in SLS or hot HSSdevices.

Polysulfones

The build material can also compositionally include a substantiallymiscible blend of one or more polyphenylsulfones (PPSU), polysulfones(PSU), and/or polyethersulfones (PES), with one or more semi-crystallinepolyaryletherketones. Preferred concentrations of thepolyphenylsulfone(s)/polysulfone(s)/polyethersulfone(s) in this blendrange from about 1% by weight to about 65% by weight, and morepreferably from about 20% by weight to about 50% by weight, where thepolyaryletherketone(s) or amorphous glycol-modified polyethyleneterephthalates (PET) constitute the remainder of the blend. Theconcentrations of the semi-crystalline polymer and the amorphous,miscible polymers or irregular monomers will be dependent upon the typeof additive manufacturing process utilized.

Polycarbonates/Polyesters

The build material can also include includes a substantially miscibleblend of one or more polycarbonates and one or more semi-crystallinepolyesters, such as polybutylene terephthalates (PBT) and/or one or moresemi-crystalline polyethylene terephthalates (PET). Preferredconcentrations of the polycarbonate(s) in this blend range from about30% by weight to about 90% by weight, and more preferably from about 50%by weight to about 70% by weight, where the polybutyleneterephthalate(s)/polyethylene terephthalate(s) constitute the remainderof the blend.

The build material can also include a substantially miscible blend ofone or more amorphous polyethylene terephthalates (e.g., glycol-modifiedpolyethylene terephthalates) and one or more semi-crystallinepolyethylene terephthalates. Concentrations of the amorphouspolyethylene terephthalate(s) in this blend range from about 10% byweight to about 40% by weight, and more typically from about 15% byweight to about 25% by weight, where the semi-crystalline polyethyleneterephthalate(s) constitute the remainder of the blend.

An advantage of utilizing PET in the alloy is that PET is relativelyinsensitive to moisture, acids and solvents in a solid state. Further,PET has a high modulus and strength or toughness. When reinforced withfor instance carbon or glass fiber, the alloy is heat resistant to over200° C. PET is also widely available, relatively inexpensive and alsorecyclable.

Relative to items built with amorphous materials using FDM techniques,unfilled PET formulations have shown superior toughness and elongationby over 25% while still exhibiting superior strength in a directionnormal to a build plane (z-direction). Carbon reinforced PET materialswhere the carbon fibers are chopped into very small pieces haveexhibited strengths over 15 ksi and moduli over 25 Msi as FDM items.Heat deflection temperatures can exceed 165° C. at 263 psi afterannealing.

For example, referring to FIGS. 9-12, the effects of utilizing PETG witha base co-polyester are illustrated. FIG. 9 is a DSC trace for the baseco-polyester (WHAT IS THE CO-POLYESTER). In FIG. 10 the baseco-polyester was modified by the addition of an impact modifier and 10wt. % PETG, which resulted in a modification in T_(g), T_(c,cold), T_(m)and the T_(c,hot). At 20 wt. % PETG in FIGS. 11 and 30 wt. % PETGfurther modification and manipulation of the T_(g), T_(c,cold), T_(m)and the T_(c,hot) occurred such that the process windows for both FDMand EP processes as well as SLS and HSS process can be manipulated andthe rate of crystallization can be controlled.

Referring to FIG. 13, 30 wt. % carbon fiber was added to theco-polyester along with 15 wt. % PETG while in FIG. 14, 40 wt. % carbonfiber was added to the co-polyester along with 10 wt. % PETG. Again themodifications to the formation of the semi-crystalline co-polyester withan amorphous and miscible secondary polymer such as PETG along with thecarbon fiber can be utilized to control the crystallization kinetics andmanipulate the process windows for both FDM and EP processes as well asSLS and HSS processes.

Ketones

The build material can also compositionally include a substantiallymiscible blend of one or more polyetherimides (PEI) and one or moresemi-crystalline polyaryletherketones (PAEK), such as one or morepolyetherketones (PEK), polyetheretherketones (PEEK),polyetherketoneketones (PEKK), polyetheretherketoneketones (PEEKK),polyetherketoneether-ketoneketones (PEKEKK), mixtures thereof, and thelike, and more preferably one or more polyetheretherketones (PEEK).Preferred concentrations of the polyaryletherketone(s) in this blendrange from about 35% by weight to about 99% by weight, and morepreferably from about 50% by weight to about 90% by weight, and evenmore preferably form about 60% by weight to about 80% by weight, wherethe polyetherimide(s) constitute the remainder of the blend.

The build material can also include a substantially miscible blend ofone or more amorphous polyaryletherketones and one or moresemi-crystalline polyaryletherketones, such as one or more amorphouspolyetherketoneketones (PEKK) and one or more semi-crystallinepolyetherketoneketones (PEKK). Concentrations of the amorphouspolyaryletherketones(s) in this blend range from about 30% by weight toabout 90% by weight, and more typically from about 50% by weight toabout 70% by weight, where the semi-crystalline polyaryletherketones(s)constitute the remainder of the blend.

In some build material compositions, the build material may also includeadditional additives, such as colorants, fillers, plasticizers, impactmodifiers, and combinations thereof. In embodiments that includecolorants, preferred concentrations of the colorants in the buildmaterial range from about 0.1% to about 5% by weight. Suitable colorantsinclude titanium dioxide, barium sulfate, carbon black, and iron oxide,and may also include organic dyes and pigments.

In build material compositions that include fillers, concentrations ofthe fillers in the build material range from about 1% to about 45% byweight for some fillers (e.g., glass and carbon fillers), and up toabout 80% by weight for other fillers, such as metallic and ceramicfillers. Suitable fillers include calcium carbonate, magnesiumcarbonate, glass spheres, graphite, carbon black, carbon fiber, glassfiber, talc, wollastonite, mica, alumina, silica, kaolin, siliconcarbide, zirconium tungstate, soluble salts, metals, ceramics, andcombinations thereof.

In the build material compositions including the above-discussedadditional additives, the polymer blend preferably constitutes theremainder of the build material. As such, the polymer blend mayconstitute from about 55% to 100% by weight of the build material, andmore preferably from about 75% to 100% by weight. In some embodiments,the polymer blend constitutes from about 90% to 100% by weight of thebuild material, more preferably from about 95% to 100% by weight. Infurther embodiments, the build material consists essentially of thepolymer blend, and optionally, one or more colorants and/oranti-oxidants and/or heat absorbing materials which typically areutilized with EP, SLS and HSS techniques.

In particular PEKK is a useful semi-crystalline polyaryletherketonesPAEK relative to PEEK and PEK because PEKK has a higher T_(g) andimproved thermo-oxidative stability relative to PEEK. Further, PEKK hasexcellent chemical resistance and high strength and stiffness, evenwithout reinforcement additives.

When formulating a PEKK semi-crystalline build material, PEKKco-polymers of differing T/I ratios and viscosities can be blended toachieve balances between toughness, crystallinity and thermalcapabilities. Stabilizers and fibrous fillers including, but not limitedto, glass and carbon can be added to improve physical properties whileinorganic agents can be added to manipulate the crystallinity of thebuild material. Exemplary inorganic agents include titanium dioxide,talc, mica, boron nitrate (BN), calcium carbonate, phosphates, sulfates,salts and combinations thereof. Referring to FIG. 15, PEKK sold byArkema Inc. located in Phillidephia, Pa. under the Kepstan® 6003designation was utilized with BN as a nucleator. As illustrated, an HHSsystem could print items in the T_(g) to the T_(c,hot) range. However,an item using the same formulation could not be printed with an SLStechnique because the energy required to melt the polymer with a laserwould burn the material. HSS techniques allow for the modification ofthe temperature profile to be more gradual, then followed by a rapidcooling to the recited range.

Referring to FIGS. 16 and 17, an alloy of Kapstan® 6000 and 8000designation manufactured by Arkema was blended with 2 parts of Kapstan®6000 to one part Kapstan® 8000 with BN utilized as a nucleator. FIGS. 16and 17 illustrate that this alloy could potentially be utilized at about325° C. which is above the lower melting point of the polymer, providedthe crystallite is in the proper ratio.

All of the above mentioned polymer blends are also substantiallyhomogenous, allowing each portion of the build material used in anadditive manufacturing system to consistently exhibit the same thermaland physical properties. As such, if the polymer blend were otherwisenon-homogenous, the build material would not be uniform. Additionally, anon-homogenous blend may result in imbalances in the crystallizationkinetics of the build material, which could reduce the above-discussedbenefits of controlling the crystallization kinetics. Further,non-miscible alloys are only strong as the interfacial adhesion betweenthe two phases in the Z-axis meaning that non-miscible alloys are weakin the Z-direction. As such, miscible alloys or copolymers withcontrolled crystalline kinetics are desired. Accordingly, feed stock ofthe build material is preferably manufactured from a build materialhaving a substantially homogenous polymer blend of the semi-crystallinepolymer(s) and the secondary material. In embodiments that include oneor more additives, the additive(s) are preferably dispersed in thepolymer blend in a substantially uniform manner.

As mentioned above, the above-discussed method may also be utilized withelectrophotography-based additive manufacturing systems, selective lasersintering systems and high speed sintering systems. With respect toelectrophotography-based additive manufacturing systems, the buildmaterial may be provided in powder form for use in anelectrophotography-based additive manufacturing system, such as thosedisclosed in Hanson et al., U.S. Publication Nos. 2013/0077996 and2013/0077997, and Comb et al., U.S. Publication Nos. 2013/0186549 and2013/0186558, the disclosures of which are incorporated by reference tothe extent that they do not conflict with the present disclosure.

As discussed in these references, the electrophotography-based additivemanufacturing systems preferably operate with layer transfusionassemblies that transfuse each successively-developed layer based oninterlayer polymer entanglement (i.e., reptation). As such, theabove-discussed method for controlling the crystallization kinetics ofthe build material for the extrusion-based additive manufacturingsystems may also be used in the same manner with theelectrophotography-based additive manufacturing systems.

In comparison, however, SLS and HSS systems may print 3D items in whichis held in a gelatinous, undercooled amorphous state between the hotmelting temperature and the hot crystallization temperature of the nylonmaterial. However, many semi-crystalline materials, such as nylonmaterials, typically have small temperature windows between theirmelting temperatures and the hot crystallization temperatures, renderingit difficult to hold the printed layers in this amorphous state afterbeing melted with a laser beam.

As discussed above, it has been found that the substantially miscibleblends for the build material of the present disclosure decrease the hotcrystallization temperature T_(c,hot) of the build material from that ofthe semi-crystalline polymer(s). Conversely, the melting temperatureT_(m) of the build material remains substantially unchanged. As such,the substantially miscible blend for the build material widens theoperating window, referred to as operating window 83 in FIGS. 4 and 5,in which the printed layers may be held in the gelatinous, undercooledamorphous state to prevent warping and distortions. In this case, thepowder materials may be selectively melted with the laser beam and heldwithin this operating window 83 until the printing operation iscompleted. The whole 3D item 30 may then be cooled down in aconventional manner.

In embodiments involving the above-discussed technique used in aselective laser sintering system (e.g., systems disclosed in Deckard,U.S. Pat. Nos. 4,863,538 and 5,132,143), the build material may beprovided in powder form for use in other powder-based additivemanufacturing systems. In some alternative embodiments, such as withsome polyamide materials (e.g., glass-filled PA6/10 materials), thistechnique may also be utilized in extrusion-based and/orelectrophotography-based additive manufacturing systems. This canaccordingly produce 3D items having high heat deflection temperatures,which can be beneficial for use with soluble support materials.

HHS systems operate in a similar manner as SLS systems. However, heat issupplied to the material through radiation on thermal sources such asinfrared (IR) heat, HHS devices and methods are disclosed in HopkinsonU.S. Pat. No. 7,879,282.

Referring to FIG. 18, the method of the present disclosure isillustrated at 100. In step 102, the technique used for additivemanufacturing is selected. A non-exhaustive list of techniques includesextrusion based techniques, such as FDM, BAAM and OOO; EP, SLS and HSS.

At step 104, the semi-crystalline material to be utilized to build theitem is identified and the crystallization kinetics of thesemi-crystalline material is identified. In the event that thecrystallization kinetics require modification such that the heat offusion is between about 2 J/g heat of fusion and about 80% of the heatof fusion of a build material that is compositionally about 100% of thesemi-crystalline build material, as measured by differential scanningcalorimetry (DSC) when cooling from the melting temperature to the hotcrystalline temperature at a rate of 10° C./min, a decision is requiredto either retard or accelerate the crystallization kinetics to utilize abuild material that is within the identified heat of fusion range. Thedetermination of whether to accelerate or retard the crystallizationkinetics can be determined by obtain a DSC trace from a solid form to amelt temperature and cooled back to a temperature through which thematerial crystallizes using the DSC technique as described herein.However, other measurements and testing techniques besides DSC can beused to determine the heat of fusion of a particular semi-crystallinematerial.

Upon determining that the crystallization kinetics required to be slowedor retarded, a secondary material is added producing a build materialthat maintains the heat of fusion in the above-disclosed range duringcrystallization at step 106. Typically, the secondary material can be acompletely miscible, amorphous polymer to form the modified buildmaterial. Additionally, direct polymerization or selection of speciallypolymerized polymers, which are synthesized with disrupted structuralregularity can be utilized. However, the present disclosure is notlimited to the above-listed secondary materials.

At step 108, a DSC trace is obtained to determine the T_(g), T_(c,cold),T_(m), and T_(c,hot) on the modified build material. From the DSC traceon the modified semi-crystalline material, process conditions can bedetermined for extrusion based additive techniques, such as FDM, BAAMand OOO, and EP additive techniques by maintaining the material betweenapproximately between about T_(g) and about T_(c,cold) and in the caseof SLS or HSS the process conditions are maintained slightly belowT_(m), and about T_(c,hot) in step 110. The amount of crystal formationin the build material is determined based upon the process conditionsused, as the amount of crystal formation is on a continuum between thelow temperature range and the high temperature range for both types ofadditive manufacturing techniques.

The item is then built in step 112 by the additive manufacturingtechnique identified in step 102. Optionally, post build processingsteps can be conducted, including, but not limited to additionalannealing in step 114.

Upon determining that the crystallization kinetics requires to beaccelerated, a secondary material is added produce a build material thatmaintains the heat of fusion in the above-disclosed range duringcrystallization at step 116. Typically, the secondary material includethe addition of micron-scale additives, such as synthetic fibers,minerals (natural or synthetic), or by the addition of one or moreimmiscible secondary polymers, which are finely dispersed as a discretephase through compounding techniques common in polymer processing.However, the present disclosure is not limited to the above-listedsecondary materials.

At step 118, a DSC trace is obtained under conditions described in step108. From the DSC trace obtained in step 118, process conditions areidentified in step 120 for a selected additive manufacturing techniquedescribed in step 110. The item is built in step 122 as described instep 112 and optional, post build processing steps can be conducted instep 124 as described in step 114.

EXAMPLES

The present disclosure is more particularly described in the followingexamples that are intended as illustrations only, since numerousmodifications and variations within the scope of the present disclosurewill be apparent to those skilled in the art. Unless otherwise noted,all parts, percentages, and ratios reported in the following examplesare on a weight basis, and all reagents used in the examples wereobtained, or are available, from the chemical suppliers described below,or may be synthesized by conventional techniques.

Example 1

A series of items were using an FDM printing technique where a FORTUS400MC machine manufactured by Stratasys, Inc. located in Eden Prairie,Minn. was utilized. The semi-crystalline build materials being tested inthis Example included a co-polymer ofpoly(oxy-1,4-phenyleneoxy-1,4-phenylene carbonyl-1,4-phenylene) PEEK andthe polyimide formed from4,4′-(4,4′-isopropylidene-diphenoxy)bis(phthalic anhydride) and1,3-phenylenediamine PEI.

The PEI is available commercially under the ULTEM® 1000 Resin series ofpolymers manufactured by SABIC Innovative Plastics located inPittsfield, Mass. The PEEK is available under the KetaSpire® KT-880resin series manufactured by Solvay Corporation located in Broxelles,Belgium or the Vitrex® series 90G PEEK polymer manufactured by VictrixUSA, Inc. locatedin West Conshohocken, Pa.

The materials were compounded on a twin-screw extruder Model Number ZSE18 mm lab compounder, manufactured by Leistritz Aktiengesellschaftlocated in Nuremberg, Germany at a temperature between 375° C. and 400°C. The formulations in Table 1 below were blended within 1% at thestated relative weight percentages as set forth in Table 1. After beingcompounded, the materials were extruded as strands, cooled andpelletized for further processing and analysis.

TABLE 1 wt % wt % KetaSpire wt % Carbon Fiber FORMULATION ULTEM KT-880Filler PEEK-PEI 40 40 60 0 PEEK-PEI 60 60 40 0 PEEK-PEI 70 70 30 0PEEK-PEI 70 49 21 30 CF25

The materials in Table 1 along with neat PEEK (KT-880) were subsequentlytested using DSC on a Model Number DSC 6000 manufactured byPerkinsElmer, Inc. located in Waltham, Mass. The samples were heated 30°C./min until the melting temperature was obtained. The samples were thencooled at a rate of 10° C./min. The results of the DSC testing are setforth in Table 2, where all temperatures are in degrees Celsius. It isnoted that the formulation designated PEEK-PEI 40 was reheated a secondtime and has data from the second run in parentheses.

TABLE 2 Delta Hf- % Delta Tg 1st Heat Hf upon heat of Cooling (2nd Tc,Tmelt Tmelt Tc, Tcrys fusion ref. Neat heat) cold Onset peak hot Onsetin J/g mat Neat 147 — 336 347 305 311 45  100% PEEK (KT-880) PEEK- 208252 320 335 279 289 21 46.7% PEI 40 (185) PEEK- 175 239 326 339 286 29229 64.4% PEI 60 PEEK- 163 223 327 340 290 295 33 73.3% PEI 70 PEEK- 159225 329 341 291 300 32 71.1% PEI 70 CF25

The resulting formulations illustrate the compounding PEI with PEEKreduces the heat of fusion to between 46.7 and 71.1 and that there is adirect correlation between the amount of amorphous PEI added to the PEEKand the reduction the heat of fusion. It is also noted that the changein the heat of fusion is within the disclosed range as set forth above.

A series of “tee” bars were built using the FDM additive technique wherea nominally dense (>90% fill) “tee” bar is built with a second,removable material support structure to test the curl of the disclosedformulations. After annealing the “tee” bars for an additional amount oftime, such as more than 4 hours after the build, the “curl” of eachsample was is measured at the extreme ends of the sample (corners),after removal of the support material and the sample is cooled to roomtemperature.

It should be noted that an acceptable level of curl is 1% over thelength of the sample. Thus, for a 15 inch bar, a curl result of 15 milsor less is desired. Further, temperature gradients and buildinaccuracies in R&D-scale materials and systems can lead to non-uniformresults for one side of the bar vs. the other. The results of the “curl”test are set forth in Table 3, below.

TABLE 3 Environment Temp Set-Point [° C.]/Approx. Actual Right SideFormulation [° C.] Curl [mil] Left Side Curl [mil] PEEK-PEI 40 225/21014.5 9.0 PEEK-PEI 70 225/210 6.5 4.5 CF25 PEEK-PEI 70 190/180 15 18 CF25

The data in Table 3 illustrates that where dimensional accuracy iscritical, a PAEK (PEEK-PEI) material with substantially reducedcrystallinity is preferred, at least where larger parts and highertemperatures are involved. In the more crystalline sample, even withsubstantial fiber filler, it was determined that the higher oven(quench) temperature of 225° C. allows too much crystallinity (stressand shrinkage) to develop to meet acceptable curl standards. Thus, alower oven temperature is preferred, as this will help to quench out anadditional fraction of the potential crystallinity, thus reducingoverall shrinkage, and giving better dimensional control in aformulation that consists substantially of PEEK.

The materials were then tested for out of build plane strength(z-strength) when build an item using the FDM build technique. Thesamples were built using single FDM beads/roads with aspect ratio (widthto height) between 2:1 and 3:1. All samples were printed with aliquefier temperature between 390 and 420° C., and at an appropriatetemperature to control curl in large parts. The exception is neat PEEKwhich was printed at 155° C. In all cases the layer Resolution was 10mil. The results of this test are set forth in Table 4, below.

TABLE 4 Bead Width Z-load [lbs- Z-strength at % Elongation Material[mil] force] Break [psi] at Break PEEK-KT- * * * * 880* Neat 22 52.39040 3.3 ULTEM 1010 PEEK-PEI 21 50.9 9550 3.7 40 PEEK-PEI 20 38.43 75602.4 60 PEEK-PEI 21 26.1 4800 2.4 70 CF25 PEI CF25 27 24.1 3470 2.8 *Anacceptable printed could not be printed in this Example for testing.

A major increase in Z-strength up to and over PEI by itself with theaddition of 40% PEEK to PEI for predominantly PEEK alloys was observed.Further, it was observed that a reduction in the rapid crystallizationinherent to PEEK alone has increased Z-strength significantly over thebase PEEK, which could not successfully be built. For pure PEEK even inan environment kept at or below its T_(g), the self-lamination strengthis so weak that moderate stresses from differential shrinkage are enoughto peel layers apart. It is believed this result occurs because PEEKcrystallizes so fully and so rapidly that each subsequent layer ofdeposited material cannot input enough additional heat into the previouslayer to fully re-melt all the crystallites and allow for meaningfulinterpenetration (diffusion/reptation) of polymer molecules.

The retardation of the crystallization of the build material, especiallyat low temperatures, is important for annealing parts to relievestresses that lead to curl, in a semi-amorphous or pseudo-amorphousstate in the FDM and/or EP additive techniques. FIG. 19 illustrates thecrystallization half times, i.e. the time to reach a peak in theexotherm for recrystallization indicative of reaching approximately 50%of the material's full level of crystallinity. Each of the PEEK-PEIalloys were rapidly heated at a rate of 100° C./min to the isothermtemperature followed by a hold for up to 12 hours. PEEK data wasobtained from the literature. It was observed that compounding PEEK withjust 20% PEI has a marked effect on the crystallization behavior ofPEEK. It is noted that the tested compositions in Example 1 are notexhaustive and that system optimization and “tuning” of build parameterscan further enhance the positive effects, including solidificationwithout excessive crystallization, leading to better layer to layerbonding, and the ability to tailor the crystallinity in the finisheditem by enlarging a post-process annealing window at a highertemperature than the build temperature.

Example 2

Example 2 illustrates that with some semi-crystalline build materialsthe crystallization kinetics are required to be accelerated to provide asuitable printed item. Acceleration of the crystallization kinetics canbe advantageous when using polyetherketoneketone PEKK as a buildmaterial. PEKK is commercially available as a series of copolymers basedon a chemistry in which “straight” co-monomers, i.e. 1,4 or parasubstituted moieties may be substituted for “kinked” co-monomers, i.e.1,3 or meta substituted moieties which can be introduced carefully (andunder manufacturer's proprietary techniques) to reduce the melting pointof a purely 1,4 substituted material. A purely 1,4 phenylene polymerizedpolymer has a melting point near 400° C., which is also in a range wherematerial viscosity becomes unstable, and thermal degradation begins tooccur relatively rapidly. Thus, using such a technique to lower thepolymer's melting point is useful. It is also useful in additivemanufacturing processes, as a side effect of the copolymerization is areduction in melting point, and also a reduction in recrystallizationtemperatures and crystallization rates, both upon heating and cooling.

In Example 2, the materials utilized are Solvay KetaSpire KT-880 PEEK asdiscussed in Example 1 and Kepstan® 5050 and 6003 and Kepstan® 8002PEKKs all manufactured by Arkema Inc. located in Philadelphia. Pa.

The materials were compounded on a twin-screw extruder Model Number ZSE18 mm lab compounder, manufactured by Leistritz Aktiengesellschaftlocated in Nuremberg, Germany at a temperature between 375° C. and 400°C. The formulations in Table 5 below were blended within 1% at thestated relative weight percentages as set forth in Table 5. After beingcompounded, the materials were extruded as strands, cooled andpelletized for further processing and analysis.

TABLE 5 wt % Material PEEK wt % PEKK 60 wt % PEKK 80 PEEK HF 100  — —PEKK 60 — 100  — HF PEKK 80 — — 100  MF PEKK — 50 50 5050 PEKK — 65 356535 PEKK N1 1 99 — PEKK N3 5 95 —

The materials in Table 5 were subsequently tested using DSC on ModelNumber DSC 6000 manufactured by PerkinsElmer, Inc. located in Waltham,Mass. The samples were heated 30° C./min until the melting temperaturewas obtained. The samples were then cooled at a rate of 10° C./min. Theresults of the DSC testing are set forth in Table 6, where alltemperatures are in degrees Celsius.

TABLE 6 FDM % Delta Hf Oven +/− Tc, Tmelt Tmelt Tc, Tc, SLS Delta TDelta upon Cooling Material Tg 10 C. cold Onset PEAK HOT Onset WindowMelt SLS Hf ref. Neat mat PEEK 147 — — 336 347 305 311 15 31 326 45 100% HF PEKK 158 160 220 300 307 220 — — 80 — 1.5   3% 60 HF PEKK 160 —— 340 360 299 309 21 41 327 51  100% 80 MF PEKK 156 182 234 327 351 289302 15 38 317 31 60.8% 5050 PEKK 157 187 246 309 345 279 294  5 30 30422 43.1% 6535 PEKK 156 189 254 285 305 230 265 10 55 278 1  2.0% N1 PEKK156 181 230 267 301 235 262  0 32 267 17 33.3% N3

The DSC results from Table 6 illustrate that it is possible toappreciably modify the crystallization behavior of pseudo-amorphous PEKKto achieve similar crystallinity reductions as in the PEEK-PEI alloysdescribed in Example 1. In these cases, acceleration of the “slow”Kepstan 6003 is the desired result. One strategy involves the additionof a much more crystalline, and more rapidly crystallizing PEKKcopolymer, Kepstan® 8002. In the 6535 and 5050 copolymers, it wasobserved that the addition of the Kepstan® 8002 PEKK can increase therelative crystallinity of a blend based on Kepstan® 6003 to between 43and 61 percent of the enthalpy observed cooling at 10 C from the meltvs. the neat Kepstan® 8002 material.

Another strategy that can be employed to increase the crystallizationrate and amount of the Kepstan® 6003 polymer was to introduce a lesscompatible polymer, such as, but not limited to, PEEK, which shouldcrystallize more rapidly, and exist as a discrete phase that“precipitates from solution” upon cooling from the melt. The above DSCdata shows that a 5% PEEK loading has increased the relativecrystallinity of a PEKK copolymer from 3% to as much as 30%. Therelatively low result in the 1% PEEK alloy may be due to the low loadinglevel, incomplete mixing, or a slight degree of miscibility between thetwo polymers that necessitates adding much higher levels to achieveappreciable effects.

Referring to FIG. 20, dynamic mechanical analysis (DMA) of theformulations designated N1 and N3 in Table 5 provides evidence ofenhanced crystallinity and crystallization rate through modulusdevelopment during when a temperature is increased over time. The datain FIG. 20 illustrates slight, and subtle differences between 1% and 5%PEEK alloys with Kepstan 6003 (N1 and N3). The data graphicallyillustrate that the 5% PEEK loading was more effective in increasingmodulus at temperatures approaching and exceeding the T_(g), which isimportant for FDM part construction and annealing. If the modulus of thepart were only slightly above the T_(g), excessive part warping anddistortion would occur from annealing processes. The following data alsographically illustrates that increasing oven temperature (quenchtemperature) can subtly, but significantly affect the modulus of theprinted parts, thus allowing them to be printed in an environment thatis above the T_(g) of the semi-crystalline polymer, but below themelting point.

Example 3

Example 3 relates to a copolyester build material that utilizescrystalline kinetics control to build items through additivemanufacturing. A semicrystalline copolyester with a melting point of240° C. was used along with a glycol modified amorphous PET (PETG) andan impact modifier. Exemplary materials used in Example 3 were SkyPET BRClear, SK Chemical SkyGreen PETG both of which are manufactured by SKChemicals located in Gyeonggi-do, South Korea, and DuPont Elvaloy® PTW.

The materials were compounded on a twin-screw extruder Model Number ZSE18 mm lab compounder, manufactured by Leistritz Aktiengesellschaftlocated in Nuremberg, Germany extruder at 270° C. for a selected amountof time, quench cooled into water, and pelletized for furtherprocessing. In this example, only a single material was tested, aformulation consisting of 76% SkyPET, 19% SkyGREEN and 5% Elvaloy PTW.

Samples were printed on a FORTUS® 400MC machine at oven set-pointtemperatures from 90° C. to 120° C. in 10° C. increments. The liquefierset-point was 320° C., and the layer resolution was 10 mils. DMA testingof modulus vs. temperature were collected on 50 mm long samples printedat each temperature. The temperature was increased from about 30° C., to150° C. This temperature range encompasses the full useful range of anunreinforced PET material, and captures the onset of additionalcrystallization (annealing). The results of the DMA testing areillustrated in FIGS. 21 and 22.

Next the formulations set forth in Table 7 as set forth below werecompounded and tested.

TABLE 7 Material 1 2 3 SkyPET BR Clear 85.5 76 66.5 PET (wt. %) ElvaloyPTW(wt. %) 5 5 5 Flat Glass, CSG-3pa- 830 (wt. %) SkyGreen PETg 9.5 1928.5 (wt. %)

The second compound formation in Table 7 was subjected to similar DMAtesting as disclosed above for the results in FIGS. 21 and 22. FIG. 23illustrates that the modulus differences for the second formulation ofTable 7 in a similar. The annealed sample was annealed for 4 hours in aseparate oven at 145° C.

While the formulations of the semi-crystalline co-polyester in Table 7range from 66.5 wt. % to 85.5 wt. % and the glycol modified amorphousPETG ranges from 9.5 wt. % to 28.5 wt. % in this example, the range ofthe semi-crystalline co-polyester can range from about 50 wt. % to about99 wt. % and the PETG can range from about 1 wt. % to about 50 wt. %.More particularly, the range of the semi-crystalline co-polyester canrange from about 55 wt. % to about 95 wt. % and the PETG can range fromabout 2 wt. % to about 45 wt. %. More particularly, the range of thesemi crystallization polymer ranges from about 75 wt. % to about 85 wt.% and for PETG ranges from about 15 wt. % to about 25 wt. %. Whateverthe formulation, any formulation that includes semi-crystallineco-polyester and PETG that has 2 J/g heat of fusion and about 80% of theheat of fusion of a semi-crystalline co-polyester that iscompositionally about 100% of the semi-crystalline co-polyester, asmeasured by differential scanning calorimetry (DSC) as set forth hereinfalls within the scope of the present disclosure whether or not fillers,binders, impact modifiers, colorants or the like are added to theformulation.

The compound formations disclosed in Table 7 were also subjected to DSCtesting. FIGS. 24-26 illustrate DSC traces for compounds 1-3 of Table 7,respectively. The T_(g), T_(c,cold), T_(m), T_(c,hot) designationsillustrate the changing process windows 120 and 122 for both extrusionbased additive manufacturing and EP at 120 and for SLS an HSS additivemanufacturing techniques at 122. The DSC scans were completed withunannealed pellets, heated at 30° C./min, and cooled at 10° C./min. Ofnote is the gradually decreasing, broadening, and low-temp shiftedrecrystallization (hot recrystallization) peaks in each of theformulations with increasing PETG content relative the basesemi-crystalline co-polyester. This indicates that a larger processingwindow can be created when utilizing SLS and HSS additive manufacturingtechniques.

As illustrated in the data and the associated FIGS. 24-26, thecombination of the semi-crystalline co-polyester and the PET reduces theT_(g) of the alloy. Interestingly, when using OOO additive manufacturingtechniques, the printed item results in a lower residual stress. If thesemi-crystalline co-polyester and the PET is annealed the heatdeflection temperature (HDT) will be significantly increased, even ifbuilt in with an OOO additive manufacturing system provide a reinforcingmaterial is added, such as carbon fiber.

Further, it is contemplated that an 80 wt. % semi-crystallineco-polyester and a 20 wt. % PET copolymer where the materials arevirgin, if processed into a powder, could be used in SLS and HSS. Thefeed heater in an SLS application would be at about 146° C., the partbed heater would be at 210° C., the cylinder heater would be at about140° C., the piston heater would be at about 169° C., the fill laserpower would be about 67 W with two bars and about 57 W with one bar, thefill scan speed would be about 500 in/sec, the outline laser power wouldbe about 14 W. Under these process conditions, or similar conditions, asemi-crystalline product could be produced with an SLS device. Applicantsubmits that the same composition, if properly ground and including aheat absorbing material could be used to print a semi-crystalline itemwith an HSS device.

Referring to FIGS. 27-29, Video Enhanced Microscopic images taken with aKeyence Microsope illustrate fracture surface of items made withdifferent materials utilizing the disclosed controlled crystallizationkinetics. FIG. 27 is a Video Enhanced Microscopic image of an itemprinted with polyamide under the trade designation PA 650 manufacturedby Advanced Laser Systems, LLC located in Temple, Tex. FIG. 28 is aVideo Enhanced Microscopic image of an item printed with polyethyleneterephthalate (PET). FIG. 29 is Video Enhanced Microscopic image of anitem printed with a copolymer of PA12 with TR90.

Due to the controlled crystallization kinetics, the material does notcrystallize as fast, and the material is allowed to stay molten forlonger. As such items printed with controlled crystallization kineticsare more dense, while maintaining feature definition.

While others may be able to achieve the densities achieved with thecontrol crystallization kinetics, other processes will lose downwardfacing definition and aesthetics.

The present disclosure allows an SLS device to produce an item withisotropic properties and with feature detail. Currently SLS devicescannot print an item with isotropic properties and feature detail.Rather one is compromised for the other

Due to the suppression of the hot crystallization temperature using theformulations set forth herein, the part bed can be maintained at lowertemperatures, and have a higher gradient between the powder temperatureand the lasered part, without worrying about feature growth. As such asillustrated in FIGS. 27-29, the present disclosure provides superiorprinted items relative to parts printed with semi-crystalline polymerswithout the secondary material.

Although the present disclosure has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the disclosure.

1. A method for printing a three-dimensional part with an additivemanufacturing system, the method comprising: providing a consumablefeedstock material comprising a semi-crystalline polymer containing oneor more secondary materials, wherein the consumable feedstock materialhas a process window in which crystalline kinetics are eitheraccelerated or retarded; melting the consumable feedstock material inthe additive manufacturing system; and forming at least a portion of thethree-dimensional part from the melted consumable feedstock material ina build environment maintained within the process window.
 2. The methodof claim 1 and further comprising: maintaining the build environment atan annealing temperature that within the process window.
 3. The methodof claim 1 and after determining that the crystallization kinetics areto be retarded, the method further comprising: causing a sufficientamount of the one or more secondary materials to be added to the buildmaterial such that an enthalpy of the build material with the secondarymaterial is between about 2 J/g heat of fusion and about 80% of the heatof fusion of the build material that is compositionally about 100% ofthe semi-crystalline build material, as measured by differentialscanning calorimetry (DSC) when cooling from the melting temperature tothe hot crystalline temperature at a rate of 10° C./min.
 4. The methodof claim 1 and wherein the secondary material comprises a substantiallyamorphous polymer that is miscible with the semi-crystalline buildmaterial.
 5. The method of claim 1 and the semi-crystalline material ismodified for direct polymerization wherein a structure of thesemi-crystalline polymer is disrupted to hinder the crystallizationkinetics such that the secondary material is not necessary.
 6. Themethod of claim 1 and wherein a process window comprises a range betweena solidification temperature below a glass transition temperature and acold crystallization temperature of the build material with thesecondary material when utilized with fused deposition modeling, out ofoven fused deposition modeling, big area additive manufacturing andelectrophotography additive techniques.
 7. The method of claim 6 andfurther comprising selecting conditions within the process window tocause a selected amount of crystallinity to form within the buildmaterial and the secondary material.
 8. The method of claim 1 andwherein the process window comprises a range between a melt temperatureand a hot crystallization temperature of the build material with thesecondary material when utilized with selective laser sintering or highspeed sintering techniques wherein the hot crystallization temperatureis lowered by at least three ° C. relative to neat semi-crystallinepolymer such that a range of temperatures in the process window isincreased.
 9. The method of claim 8 and further comprising selectingconditions within the process window to cause a selected amount ofcrystallinity to form within the build material and the one or moresecondary material.
 10. The method of claim 1 and after determining thatthe crystallization kinetics are to be accelerated, the method furthercomprising: causing a sufficient amount of the one or more secondarymaterials to be added to the build material such that an enthalpy of thebuild material with the secondary material is at least 5 J/g when cooledat 10° C./min cooling as measured by differential scanning calorimetry(DSC) when cooling from the melting temperature to the hot crystallinetemperature at a rate of 10° C./min.
 11. The method of claim 10 andwherein the secondary material comprises synthetic fibers or minerals.12. The method of claim 10 and wherein the secondary materials comprisesa second polymer that is immiscible with the build material.
 13. Themethod of claim 1 and wherein the addition of the secondary material tothe semi-crystalline build material such that at least a 3° C.suppression of a hot crystallization temperature is realized and theprocess window between the melt temperature and the hot crystallizationtemperature increases.
 14. The method of claim 1 and wherein theaddition of the secondary material to the semi-crystalline buildmaterial such that at least a 5° C. suppression of a hot crystallizationtemperature is realized and the process window between the melttemperature and the hot crystallization temperature increases.
 15. Themethod of claim 1 and wherein the addition of the secondary material tothe semi-crystalline build material such that at least a 10° C.suppression of a hot crystallization temperature is realized and theprocess window between the melt temperature and the hot crystallizationtemperature increases.
 16. A method for printing a three-dimensionalitem with an additive manufacturing system, the method comprising:providing a consumable feedstock material comprising a semi-crystallinepolymer containing one or more secondary materials that are configuredto retard crystallization of the one or more semi-crystalline polymers,wherein the consumable feedstock material has a process window in whichcrystalline kinetics are retarded and wherein the consumable feed stockhas an enthalpy of the consumable feedstock is between about 2 J/g heatof fusion and about 80% of the heat of fusion of the build material thatis compositionally about 100% of the semi-crystalline build material, asmeasured by differential scanning calorimetry (DSC) when cooling fromthe melting temperature to the hot crystalline temperature at a rate of10° C./min; melting the consumable feedstock material in the additivemanufacturing system; and forming at least a portion of thethree-dimensional part from the melted consumable feedstock material ina build environment maintained within the process window.
 17. The methodof claim 16 and wherein the one or more secondary materials comprises asubstantially amorphous polymer that is miscible with thesemi-crystalline build material.
 18. The method of claim 16 and whereina process window comprises a range between a solidification temperaturebelow a glass transition temperature and a cold crystallizationtemperature of the build material with the secondary material whenutilized with fused deposition modeling, out of oven fused depositionmodeling, big area additive manufacturing, cool high speed sintering andelectrophotography additive techniques.
 19. The method of claim 16 andwherein a process window comprises a range between a melt temperatureand a hot crystallization temperature of the build material with thesecondary material when utilized with selective laser sintering or hothigh speed sintering techniques.
 20. The method of claim 16, the hotcrystallization temperature is suppressed at least about 3° C. to expandthe process window relative to neat semi-crystalline polymer.
 21. Amethod for printing a three-dimensional item with an additivemanufacturing system, the method comprising: providing a consumablefeedstock material comprising a semi-crystalline polymer containing oneor more secondary materials that are configured to retardcrystallization of the one or more semi-crystalline polymers, whereinthe consumable feedstock material has a process window in whichcrystalline kinetics are retarded and wherein the consumable feed stockhas an enthalpy of the consumable feedstock is at least 5 J/g whencooled at 10° C./min cooling as measured by differential scanningcalorimetry (DSC) when cooling from the melting temperature to the hotcrystalline temperature at a rate of 10° C./min; melting the consumablefeedstock material in the additive manufacturing system; and forming atleast a portion of the three-dimensional part from the melted consumablefeedstock material in a build environment maintained within the processwindow.
 22. The method of claim 21 and wherein the secondary materialcomprises synthetic fibers or minerals.
 23. The method of claim 21 andwherein the secondary materials comprises a second polymer that isimmiscible with the build material.
 24. A method for printing athree-dimensional item with an additive manufacturing system, the methodcomprising: providing a consumable feedstock material comprising asemi-crystalline polymer containing one or more secondary materials thatare configured to retard crystallization of the one or moresemi-crystalline polymers, wherein the consumable feedstock material hasa process window in which crystalline kinetics in which a hotcrystallization temperature is suppressed at least 3° C. relative toneat semi-crystalline polymer; melting the consumable feedstock materialin the additive manufacturing system; and forming at least a portion ofthe three-dimensional part from the melted consumable feedstock materialin a build environment maintained within the process window.
 25. Themethod of claim 24 and wherein the secondary material comprises asubstantially amorphous polymer that is miscible with thesemi-crystalline build material.
 26. The method of claim 24 and thesemi-crystalline material is modified for direct polymerization whereina structure of the semi-crystalline polymer is disrupted to hinder thecrystallization kinetics such that the secondary material is notnecessary.